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FLASH-RT does not affect chromosome translocations and junction structures beyond that of CONV-RT dose-rates

ABSTRACT: The molecular and cellular mechanisms driving the enhanced therapeutic ratio of ultra-high dose-rate radiotherapy (FLASH-RT) over slower conventional (CONV) ionizing radiation (IR) dose-rate are not known. However, attenuated DNA damage and transient oxygen depletion are among a number of proposed models. Here, we tested whether FLASH-IR under physioxic (4% O2) and hypoxic conditions (≤2% O2) attenuates detection of genome-wide translocations relative to CONV dose rates and whether any differences identified revert under normoxic (21% O2) conditions. We employed high-throughput rejoin and genome-wide translocation sequencing (HTGTS-JoinT-seq), usingS. pyogenesandS. aureusCas9 “bait” DNA double strand breaks (DSBs), to measure differences in proximal deletions, inversions, and excision circles and their translocation to “prey” genome-wide DSBs generated by CONV (0.08-0.13Gy/s) and FLASH (1x102-5x106Gy/s) dose rates, under varying IR doses and oxygen tensions. Normoxic and physioxic IR exposure in HEK293T cells increased translocations at the cost of decreasing proximal repair but were indistinguishable between CONV and FLASH dose-rates. Although decreased numbers of translocations were recovered as cells transitioned to hypoxic (<2%) conditions, the combined decrease in oxygen tension with IR dose-rate modulation did not reveal significant differences in the level of translocations nor in junction structures, which, for proximal repair, were increased in direct and short microhomologies. We conclude that irrespective of oxygen tension, FLASH IR dose rates produce translocations and junction structures at levels that are indistinguishable from CONV dose rates.

ORGANISM(S): Homo sapiens

PROVIDER: GSE227466 | GEO | 2023/03/29

REPOSITORIES: GEO

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Project description:Following nuclear accidents and the increasing use of radionuclides, environmental radiation radiological protection is a source of major concern, particularly in the context of low doses. Ionizing radiation (IR) may lead to genetic mutations, chromosomal rearrangements and epigenetic modifications. The present study focuses on the in vivo effects of low to moderate doses of IR on zebrafish early embryonic development. The effects of IR on the transcriptome were studied at the shield stage (6 hours post-fertilization, hpf) and at dose rates from 50 mGy/h to 0.005 mGy/h. The effects on the methylome by whole genome bisulfite sequencing were investigated at the same stage and at dose rates of 50 mGy/h and 5 mGy/h.IR exposure impacted the expression of genes involved in germ layers specification during gastrulation of zebrafish embryos. Moreover, changes in mitochondrial energetic metabolism were detected at all dose rates. Different transcriptomic responses were observed between groups irradiated at the two highest dose rates, 50 mGy/h and 5 mGy/h and those irradiated at the three lower dose rates. However, the transcriptomic analysis revealed an impact of IR on development, neurogenesis and muscular development at 50 mGy/h, 5 mGy/h and 0.5 mGy/h. The global level of methylation was not changed after exposure to IR, and no widespread changes in transposable elements were detected. Rather, we observed that IR induced loci specific demethylation in the promoter of genes involved in development, neurogenesis and myogenesis. Interestingly, this promoter hypomethylation was equally associated with a change in gene expression. In this study, both DMR and gene expression analysis pointed toward a specific deregulation of genes involved in development, neurogenesis and myogenesis. The modification of the methylation pattern in promoters of genes involved in central nervous system development and muscle development seems to be responsible of transcriptomic changes. This study confirms previous results obtained at later developmental stages, showing that neurogenesis and muscle development were also impacted at 50 mGy/h, 5 mGy/h and 0.5 mGy/h with phenotypic alterations in terms of muscle histology and swimming behaviour. This suggests that early developmental perturbations are predictive of functional defects at later developmental stages.

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FLASH-RT does not affect chromosome translocations and junction structures beyond that of CONV-RT dose-rates

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