Lack of hepatic response of microRNA in mice following chronic benzo(a)pyrene exposure (miRNA)

Benzo[a]pyrene (BaP) is a very extensively studied prototypical polycyclic aromatic hydrocarbons (PAHs). Previous work in our laboratory showed no changes of microRNA (miRNA) expression in liver following a 3 days exposure to BaP, suggesting a lack of miRNA transcriptional responses to aryl hydrocarbon receptor agonists and/or DNA damage. Here, we studied 25-week old male MutaTM Mouse exposed to 25, 50, and 75 mg/kg/day BaP by oral gavage for 28 consecutive days. MAANOVA identified 110 differentially expressed genes (adjusted p < 0.05) with fold change greater than 1.5. The genes most affected included those involved in xenobiotic metabolism, phase II metabolizing enzymes, as well as the downstream targets of p53. Pathway specific RT-PCR was used to confirm the p53 response. A single significant increase in miRNA expression was identified (mir-34a and validated using the Qiagen miScript PCR system). This miRNA is known to be transcriptionally activated by p53. Ingestion of BaP leads to widespread changes in gene expression in mouse liver, with enrichment of genes involved in cell cycle arrest, DNA damage response, and apoptosis via the p53 pathway. In contrast, miRNA expression was relatively unaffected. Only miR-34a was significantly up-regulated, and may therefore play a critical role in the post-transcriptional regulation of p53 and/or its downstream targets. Keywords: Agilent mouse 8 x 15K miRNA microarray system with miRNA complete labeling and hyb kit were used to assess miRNA expression in response to 25, 50, and 75 mg/kg BaP treatment RNA samples from 3 control and 5 mice per treatment group (24mg/kg, 50mg/kg, and 75mg/kg) containing 100 ng were labelled using Agilent?s miRNA complete labelling and Hyb Kit (Agilent Tech, Mississauga, ON, Canada).