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DNA hydroxymethylation landscape and mitochondrial DNA in lung fibroblasts exhibit specific signatures of single- and multi-fraction alpha-particle radiation

ABSTRACT: Alpha (α)-radiation is a genotoxic and epigenotoxic agent capable of increasing cancer and other health risks. Human exposure to α-radiation to unsafe levels can occur as a result of a single exposure from a nuclear incident or repetitive exposures via inhalation of naturally occurring radon gas that accumulates in enclosed spaces. DNA hydroxymethylation (DNAhm), an intermediary step between DNA methylation (DNAm) and demethylation, is an understudied epigenetic event that can modify gene expression. The human lung is susceptible to single and multiple α-radiation events, yet the DNAhm changes induced in this tissue remain unexplored. The genomic-wide DNAhm profile was examined in the 64 α-irradiated human embryonic lung fibroblast samples from our 2023 methylome study. These cells were irradiated to seven doses (N=4 per dose) of americium-241 ranging from 2 mGy to 2.2 Gy, using two exposure regimens, single-fraction (SF – total dose given at once), and multi-fraction exposure (MF – total dose equally distributed over 14 consecutive days). We report that SF and MF α-irradiation primarily increased DNAhm levels, with more alterations observed following the MF exposure: the gene body region being more susceptible to these alterations. The genes with increased DNAhm levels due to the MF exposure, contrarily to the SF, led to a profound disruption of the inflammatory response and other cellular pathway-based biomarkers of radiation in the α-irradiated cells. We also detected DNAhm changes in key genes encoding enzymes involved in DNAm / demethylation processes, which supports the previous DNAm findings. Similar to DNAm, MF α-irradiation induced a greater number of DNAhm aging changes. Compared to equivalent SF doses, the MF pro-oxidant α-irradiation also resulted in more mitochondrial damage, specifically in the hydroxymethylome of nuclear-encoded mitochondrial genes and the mitochondrial DNA copy number. Although at equivalent doses, SF and MF α-radiation exposures induce radically different effects on the DNAhm and mitochondrial DNA. The DNAhm changes help explain the effects observed in our 2023 methylome study. These findings prove that environmental exposure regimens are a major consideration when assessing DNAm and DNAhm biomarkers and the potential health effects of a pro-oxidant such as α-radiation.

ORGANISM(S): Homo sapiens

PROVIDER: GSE284411 | GEO | 2026/07/20

REPOSITORIES: GEO

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Project description:Alpha (α)-radiation is a ubiquitous environmental agent with epigenotoxic effects. Human exposure to α-radiation at potentially harmful levels can occur repetitively over the long term via inhalation of naturally occurring radon gas that accumulates in enclosed spaces, or as a result of a single exposure from a nuclear accident. Alterations in epigenetic DNA methylation (DNAm) have been implicated in normal aging and cancer pathogenesis. Nevertheless, the effects of aberrations in the methylome of human lung cells following exposure to single or multiple α-radiation events on these processes remain unexplored. Here, we performed genome-wide DNAm profiling of human embryonic lung fibroblasts from control and irradiated cells using americium-241 α-sources. Cells were α-irradiated in quadruplicates to seven doses using two exposure regimens, a single-fraction (SF) where the total dose was given at once, and a multi-fraction (MF) method, where the total dose was equally distributed over 14 consecutive days. Our results revealed that SF irradiations were prone to a decrease in methylation levels, while MF irradiations mostly increased methylation. The analysis also showed that the gene body (i.e. exons and introns) was the region mostly altered by both the SF hypomethylation and the MF hypermethylation. Additionally, the MF irradiations induced the highest number of differentially methylated regions in genes associated with DNAm biomarkers of aging, carcinogenesis, and cardiovascular disease. The DNAm profile of the oncogenes and tumour suppressor genes suggested that the fibroblasts elicited a defensive response to the MF α-irradiation. Key DNAm events of ionizing radiation exposure including changes in methyl levels in mitochondria dysfunction-related genes were mainly identified in the MF groups. However, these alterations were under-represented, indicating that the mitochondria undergo adaptive mechanisms, aside from methylation, in response to radiation-induced oxidative stress. In this study, we identified a contrasting methylomic profile in the lung fibroblasts α-irradiated to SF compared with MF exposures. These findings demonstrate that the methylome response of the lung cells to α-radiation is highly dependent on both the total dose and the exposure regimen. They also provide novel insights into potential biomarkers of α-radiation which may lead to the development of innovative approaches to detect, prevent and treat α-particle related diseases.

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DNA hydroxymethylation landscape and mitochondrial DNA in lung fibroblasts exhibit specific signatures of single- and multi-fraction alpha-particle radiation

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