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Global gene expression responses to low doses of protons in a human 3-dimensional skin model

ABSTRACT: Accumulating data suggest that the biological responses to high and low doses of radiation are qualitatively different, necessitating the direct study of low dose responses. Most such studies have utilized 2-dimensional culture systems, which may not fully represent responses in 3-dimensional tissues. To gain insight into low dose responses in tissue, we have profiled global gene expression in EPI-200, a 3-dimensional tissue model that imitates the structure and function of human epidermis, at 4, 16 and 24 hours after exposure to high (2.5 Gy) and low (0.1 Gy) doses of low LET protons. The most significant gene ontology groups among genes altered in expression were consistent with effects observed at the tissue level, where the low dose was associated with gradual recovery and tissue remodeling, while the high dose resulted in loss of structural integrity and terminal differentiation. Network analysis of the significantly responding genes suggested that TP53 dominated the response to 2.5 Gy, while HNF4A, a novel transcription factor not previously associated with radiation response, was most prominent in the low dose response. Thus, these studies address the molecular basis of response to low versus high dose low LET radiation exposure.

ORGANISM(S): Homo sapiens

PROVIDER: GSE20629 | GEO | 2010/06/01

SECONDARY ACCESSION(S): PRJNA124843

REPOSITORIES: GEO

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Project description:Purpose: The International Commission on Radiological Protection (ICRP) recently recommended reducing the occupational equivalent dose limit for the lens of the eye. Based primarily on a review of epidemiological data, the absorbed dose threshold is now considered to be 0.5 Gy for induction of acute opacities, reduced from the previous threshold of 2 Gy. However, direct mechanistic evidence to support an understanding of the underlying molecular mechanisms of damage is still lacking. To this end, we explored the effects of a broad dose-range of ionizing radiation exposure on gene expression changes in a human lens epithelial (HLE) cell-line in order to better understand the shape of the dose-response relationship and identify transcriptional thresholds of effects. Methods: HLE cells were exposed to doses of 0, 0.01, 0.05, 0.25, 0.5, 2, and 5 Gy of X-ray radiation at two dose rates (1.62 cGy/min and 38.2 cGy/min). Cell culture lysates were collected 20 h post-exposure and analysed using whole-genome RNA-sequencing. Pathways and dose-thresholds of biological effects were identified using benchmark dose (BMD) modeling. Results: Transcriptional responses were minimal at doses less than 2 Gy. At higher doses there were a significant number of differentially expressed genes (DEGs) (p < 0.05, fold change > |1.5|) at both dose rates, with 1308 DEGs for the low dose rate (LDR) and 840 DEGs for the high dose rate (HDR) exposure. Dose-response modeling showed that a number of genes exhibited non-linear bi-phasic responses, which was verified by digital droplet PCR. BMD analysis showed the majority of the pathways responded at BMD median values in the dose range of 1.5-2.5 Gy, with the lowest BMD median value being 0.6 Gy for the HDR exposure. The minimum pathway BMD median value for LDR exposure, however, was 2.5 Gy. Although the LDR and HDR exposures shared pathways involved in extracellular matrix reorganization and collagen production with BMD median value of 2.9 Gy, HDR exposures were more effective in activating pathways associated with DNA damage response, apoptosis, and cell cycling relative to LDR exposure. Conclusion: Overall, the results suggest that radiation induces complex non-linear transcriptional dose-response relationships that are dose-rate dependent. Pathways shared between the two dose rates may be important contributors to radiation-induced cataractogenesis. BMD analysis suggests that the majority of pathways are activated above 0.6 Gy, which supports current ICRP identified dose thresholds for deterministic effects to the lens of the eye of 0.5 Gy.

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Global gene expression responses to low doses of protons in a human 3-dimensional skin model

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