Project description:The biomedical consequences of space radiation pose a significant concern for astronauts engaged in deep space. However, the effects of long-term low dose-rate exposures in space environments remain elusive. In this study, we simulated the space radiation environment by exposing human bronchial epithelial cells to low dose-rate (0.0067 Gy/day) α-particles, and continuously irradiated them multiple times to achieve cumulative total doses of 0.2 Gy, 0.4 Gy, and 0.5 Gy, respectively. At the same time, the cells were irradiated with the same total dose in a single exposure to investigate the potential of low dose-rate alpha particles to induce malignant transformation of human bronchial epithelial cells. A comprehensive suite of assays was employed to assess tumorigenic potential, including tumor formation in NOD/SCID mice, immunohistochemistry, CCK-8 proliferation assay, invasion assay, and the evaluation of multicellular spheroid formation during subsequent passages post-irradiation. Moreover, we dissected differential malignant mechanisms in tumor evolution ecosystem induced by the two distinct irradiation modes from systems biology views based on scRNA-seq technology. Our results showed that exposure to α-particles, whether through a single acute exposure or long-term low dose-rate exposures, induced the occurrence and development of tumors. Long-term low dose-rate exposures to α-particles increase the malignancy of induced tumors, but not the risk of carcinogenesis, compared to a single acute exposure with the same total dose. In addition, through scRNA-seq, we found that long-term low dose-rate exposures triggered more copy number variation (CNV) and epithelial-mesenchymal transition (EMT) events, and the activation of DNA damage repair pathways occurred significantly later than with a single acute exposure and involved more specific changes in cellular communication dynamics. In conclusion, our findings provide emerging yet convincing evidence that not only sheds light on why cells exposed to long-term low dose-rate exposures exhibit heightened malignancy, but also offers valuable insights into the genetic determinants driving tumor evolution and heterogeneity.

Project description:Bronchial epithelial cells, which line the airway of the respiratory tract, undergo genome-wide level changes in gene expression and DNA methylation particularly when exposed to fine (< 2.5 µm) PM (PM2.5). Although some of these changes have been reported in other studies, a comparison of how different doses and duration of exposure affect both the gene transcriptome and DNA methylome has not been done. We exposed BEAS-2B, a bronchial epithelial cell line, to a single exposure of high (30 µg/cm2) or low (1 µg/cm2) dose of PM2.5 (obtained from Beijing, China in 2015) for 24 hours. We also exposed BEAS-2B cells to repeated exposures of low dose (1 µg/cm2) PM2.5 every day for seven days. We then examined the transcriptomic changes (by RNA-Seq) and DNA methylomic changes (by enhanced reduced representation bisulfite sequencing). Widespread changes in gene expression occurred after cells were exposed to a single, high dose (30 µg/cm2) exposure of PM2.5 for 24 h. These genes were enriched in pathways regulating MAPK signaling, PI3K-Akt signaling, cytokine interactions, IL6, and P53. DNA methylomic analysis showed that nearly half of the differentially expressed genes were found to also have DNA methylation changes. Cells exposed to a lower dose (1 µg/cm2) of PM2.5 demonstrated a similar, but more attenuated change in gene expression. Cells exposed to repeated doses of PM2.5 for seven days, however, demonstrated a different set of genes that were differentially expressed compared to a single exposure. The DNA methylation changes that occurred with repeated, low dose exposure were also different from single high dose exposures and skewed towards overall hypomethylation. This hypomethylation corresponded with an increase in expression of ten-eleven translocation enzymes. Overall, these data demonstrate how variations in dose and duration of PM2.5 exposure induce distinct differences in the transcriptomic and DNA methylomic profile of bronchial epithelial cells.

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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Differential Network Analysis Reveals the Key Role of the ECM-receptor Pathway in α-Particle-induced Malignant Transformation

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