Assessing molecular initiating events (MIEs), key events (KEs) and modulating factors (MFs) for styrene responses in mouse lungs using whole genome gene expression profiling following 1-day and multi-week exposures

• Published in: Toxicology and applied pharmacology Vol. 335; pp. 28 - 40
• Main Authors: Andersen, Melvin E., Cruzan, George, Black, Michael B., Pendse, Salil N., Dodd, Darol, Bus, James S., Sarang, Satinder S., Banton, Marcy I., Waites, Robbie, McMullen, Patrick D.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15.11.2017
• Subjects: Adaptation and modulating factors; Animals; Aryl Hydrocarbon Hydroxylases - genetics; Aryl Hydrocarbon Hydroxylases - metabolism; Circadian Rhythm - drug effects; Circadian Rhythm - genetics; Circadian Rhythm Signaling Peptides and Proteins - genetics; Circadian Rhythm Signaling Peptides and Proteins - metabolism; Cytochrome P-450 CYP2B6 - genetics; Cytochrome P-450 CYP2B6 - metabolism; Cytochrome P-450 Enzyme System - deficiency; Cytochrome P-450 Enzyme System - genetics; Cytochrome P450 Family 2 - genetics; Cytochrome P450 Family 2 - metabolism; Dose-Response Relationship, Drug; Gene Expression Profiling - methods; Gene Regulatory Networks - drug effects; Genotype; Inhalation Exposure - adverse effects; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; Lung - drug effects; Lung - metabolism; Male; Mice, Inbred C57BL; Mice, Knockout; MIEs; Models, Animal; Molecular initiating events; Mouse lung tumors; Nr4 family gene downregulation; Phenotype; Signal Transduction - drug effects; Signal Transduction - genetics; Styrene inhalation; Styrenes - metabolism; Styrenes - toxicity; Time Factors; Toxicogenetics - methods; Transcription Factors - genetics; Transcription Factors - metabolism; Transcriptome - drug effects; Molecular initiating events; Styrene inhalation; MIEs; Mouse lung tumors; Nr4 family gene downregulation; Adaptation and modulating factors
• ISSN: 0041-008X; 1096-0333
• DOI: 10.1016/j.taap.2017.09.015

Styrene increased lung tumors in mice at chronic inhalation exposures of 20ppm and greater. MIEs, KEs and MFs were examined using gene expression in three strains of male mice (the parental C57BL/6 strain, a CYP2F2(−/−) knock out and a CYP2F2(−/−) transgenic containing human CYP2F1, 2A13 and 2B6). Exposures were for 1-day and 1, 4 and 26weeks. After 1-day exposures at 1, 5, 10, 20, 40 and 120ppm significant increases in differentially expressed genes (DEGs) occurred only in parental strain lungs where there was already an increase in DEGs at 5ppm and then many thousands of DEGs by 120ppm. Enrichment for 1-day and 1-week exposures included cell cycle, mitotic M-M/G1 phases, DNA-synthesis and metabolism of lipids and lipoproteins pathways. The numbers of DEGs decreased steadily over time with no DEGs meeting both statistical significance and fold-change criteria at 26weeks. At 4 and 26weeks, some key transcription factors (TFs) - Nr1d1, Nr1d2, Dbp, Tef, Hlf, Per3, Per2 and Bhlhe40 - were upregulated (|FC|>1.5), while others - Npas, Arntl, Nfil3, Nr4a1, Nr4a2, and Nr4a3 - were down-regulated. At all times, consistent changes in gene expression only occurred in the parental strain. Our results support a MIE for styrene of direct mitogenicity from mouse-specific CYP2F2-mediated metabolites activating Nr4a signaling. Longer-term MFs include down-regulation of Nr4a genes and shifts in both circadian clock TFs and other TFs, linking circadian clock to cellular metabolism. We found no gene expression changes indicative of cytotoxicity or activation of p53-mediated DNA-damage pathways. •Styrene response consistent with direct mitogenicity of Cyp2F2 and Nr4a signaling•Longer term exposure show changes in circadian pathways.•Changes in circadian pathways associated with Nr4a receptor family down-regulation•Consistent changes were seen only in wild type mice.•No evidence of activation of p53-mediated DNA-damage or cell stress pathways