It was recently reported that long-term activation of CAR with phenobarbital treatment can lead to epigenetic changes at the promoter of the CAR target gene Cyp2B10 in adult mouse livers.18 Here our results reveal Metformin in vivo that transient activation of CAR during the neonatal stage is sufficient to generate a long-term epigenetic memory, which permanently changes drug metabolism in mouse livers. CAR is a central regulator of drug/xenobiotic metabolism, and CAR activation is frequently detected in a variety of therapeutics. Therefore, our results provide new insights into the potential effect of CAR activation during development on health issues for adults, such as drug
metabolism. We examined the expression of 21 CAR target genes in mouse livers harvested 3 months after neonatal CAR activation and found that transient activation of CAR during development specifically induced the mRNA levels of the CAR target genes Cyp2B10 and Cyp2C37. Consistent with these results, we found that neonatal exposure to TCPOBOP specifically caused a strong epigenetic switch from a repressive to an
active chromatin configuration at the Cyp2B10 and Cyp2C37 promoters, but not at the promoters of other CAR target genes (Figs. 3 and 4). ChIP assays suggest that H3K4 trimethylation is induced in Cyp2B10 and Cyp2C37, but not other CAR target genes at the developmental stage tested (third day after birth), and that H3K9 detrimethylation is mediated at this early developmental stage in all CAR target genes tested (Fig. 4). Interestingly, our data also LY294002 price suggest that the suppressed H3K9 trimethylation could be reversed in tested CAR target genes, except for Cyp2B10 and Cyp2C37, in 12-week-old
mouse livers. It will be interesting to reveal the mechanism of H3K4 trimethylation and reversed H3K9 demethylation in selective genes in future studies. Ligand-activated xenobiotic receptor CAR plays important roles in drug/xenobiotic detoxification, acetaminophen-induced hepatotoxicity, and hepatocyte proliferation.10, 15, 25 We found that transient Thalidomide activation of CAR by neonatal exposure to TCPOBOP resulted in a permanent increase in drug resistance in mouse livers (Table 1) but did not affect acetaminophen-induced hepatotoxicity and hepatocyte proliferation (data not shown). This may be due to the selective/permanent induction of CAR target genes in response to transient activation of CAR during development. Indeed, CAR activation on the third day after birth permanently induced the expression of Cyp2B10 and Cyp2C37, but not expression of acetaminophen-metabolizing enzymes (Cyp1A2, Cyp3A11, and GSTPi) and hepatocyte proliferation-related transcription factors c-Myc and Foxm1b (see Supporting Table 1). It is well known that H3K4 trimethylation is tightly associated with transcriptional activation and counters the repressive chromatin environment imposed by H3K9 methylation.