Pulmonary gene and microRNA expression changes in mice exposed to benzo(a)pyrene by oral gavage

Exposure to the environmental mutagen benzo(a)pyrene (BaP) alters the expression of AHR-responsive genes as well as genes involved in other pathways. We recently reported that exposure of adult mice to BaP resulted in a robust transcriptome response in the liver, but this was accompanied by a complete lack of change in microRNA (miRNA) expression. Since BaP exposure does not result in hepatocarcinogenicity, but does cause lung cancer, in the present study we examine the pulmonary mRNA and miRNA responses to BaP in the same mice. Adult male B6C3F1 mice were exposed to 150 and 300 mg/kg BaP by oral gavage for three consecutive days and sacrificed 4h after the last exposure. Serum clinical chemistry was performed for both the doses to assess the general toxicity of BaP; a modest decrease in serum inorganic phosphorous was observed at both the doses. A small decrease in serum glucose following 150 mg/kg and alkaline phosphatase following 300 mg/kg BaP was observed. BaP-DNA adduct levels in whole lung and liver tissues were assessed by (32)P post labelling and similar dose dependent increases were observed for lung and liver. Using DNA microarrays, pulmonary mRNA and miRNA expressions were analysed. Over 1000 genes were statistically differentially expressed (p<0.05). The perturbed pathways included oxidative stress, xenobiotic metabolism, cell proliferation, cell cycle, B and T-cell receptor signalling and primary immunodeficiency signalling pathways. Analysis of miRNA profiles revealed downregulation of miR-150, miR-142-5p, miR-122 and upregulation of miR-34c, miR-34b-5p and miR-29b. These miRNAs are involved in the biological processes, immune response, cell proliferation and cell cycle, which are the main pathways affected at the mRNA level. Thus, miRNAs are more responsive to BaP in lungs than in liver, and are likely to be involved in the regulation of the pulmonary responses to BaP exposure.