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Mouse strain-specific chromatin and transcriptional states modulate the DNA-damage response to an inhalational carcinogen

ABSTRACT: Genetically distinct individuals are differentially affected by the DNA damaging effects of exposure to environmental toxicants, but the mechanisms contributing to these differences are poorly understood. It is known that genetic variation affects the establishment of the gene regulatory landscape, and we hypothesized that this may significantly contribute to the observed heterogeneity in individual responses to exogenous cellular insults. In this study, we investigated how genetic variation and chromatin organization may dictate susceptibility to DNA damage. We measured DNA damage, mRNA and miRNA expression, and chromatin accessibility genome-wide in lung tissue from two genetically-divergent inbred mouse strains, C57BL/6J and CAST/EiJ, at baseline and in response to exposure to a model DNA-damaging chemical, 1,3-butadiene (BD). Our results show that unexposed CAST/EiJ and unexposed C57BL/6J mice have very different chromatin organization and transcription profiles in the lung. Importantly, in unexposed CAST/EiJ, which is more resistant to BD-induced DNA damage, we see increased transcription and a more accessible chromatin landscape around genes involved in detoxification pathways. Upon BD exposure, chromatin is significantly remodeled in C57BL/6J around these genes to more closely resemble that found in CAST/EiJ. This suggests that strain-specific differences in baseline chromatin organization and transcription contribute to the relative resistance of CAST/EiJ to the DNA damaging effects of BD. Based on these results, we propose more generally that differences in the baseline molecular state of key tissues, driven by unique genetic backgrounds, significantly contributes to inter-individual variability in response to DNA-damaging environmental agents.

ORGANISM(S): Mus musculus

PROVIDER: GSE86623 | GEO | 2017/08/29

SECONDARY ACCESSION(S): PRJNA342424

REPOSITORIES: GEO

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Project description:Epigenetic effects of environmental chemicals are under intense investigation to fill existing knowledge gaps between environmental/occupational exposures and adverse health outcomes. Chromatin accessibility is one prominent mechanism of epigenetic control of transcription, and understanding of the chemical effects on both could inform the causal role of epigenetic alterations in disease mechanisms. In this study, we hypothesized that baseline variability in chromatin organization and transcription profiles among various tissues and mouse strains influence the outcome of exposure to the DNA damaging chemical 1,3-butadiene. To test this hypothesis, we evaluated DNA damage along with comprehensive quantification of RNA transcripts (RNA-seq), identification of accessible chromatin (ATAC-seq), and characterization of regions with histone modifications associated with active transcription (ChIP-seq for acetylation at histone 3 lysine 27, H3K27ac). We collected these data in the lung, liver and kidney of mice from two genetically divergent strains, C57BL/6J and CAST/EiJ, that were exposed to clean air or to 1,3-butadiene (~600 ppm) for 2 weeks. We found that tissue effects dominate differences in both gene expression and chromatin states, followed by strain effects. At baseline, xenobiotic metabolism was consistently more active in CAST/EiJ, while immune system pathways were more active in C57BL/6J across tissues. Surprisingly, even though all three tissues in both strains harbored butadiene-induced DNA damage, little transcriptional effect of butadiene was observed in liver and kidney. Toxicologically-relevant effects of butadiene in the lung were on the pathways of xenobiotic metabolism and inflammation. We also found that variability in chromatin accessibility across individuals (i.e., strains) only partially explains the variability in transcription. This study showed that variation in the basal states of epigenome and transcriptome may be useful indicators for individuals or tissues susceptible to genotoxic environmental chemicals.

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Mouse strain-specific chromatin and transcriptional states modulate the DNA-damage response to an inhalational carcinogen

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