Time-course of transcriptomic change in the lungs of F344 rats repeatedly exposed to a multiwalled carbon nanotube in a 2-year test

Despite intensive toxicological studies of carbon nanotubes (CNTs) over the last two decades, only a few studies have demonstrated their pulmonary carcinogenicities in chronic animal experiments, and the underlying molecular mechanisms are still unclear. To obtain molecular insights into CNT-induced lung carcinogenicity, we performed a transcriptomic analysis using a set of lung tissues collected from rats in a 2-year study, in which lung tumors were induced by repeated intratracheal instillations of a multiwalled carbon nanotube, MWNT-7. The RNA-seq-based transcriptome identified a large number of significantly differentially expressed genes at Year 0.5, Year 1, and Year 2. Ingenuity Pathway Analysis revealed that macrophage-elicited signaling pathways such as phagocytosis, acute phase response, and Toll-like receptor signaling were activated throughout the experimental period. At Year 2, cancer-related pathways including ERBB signaling and some axonal guidance signaling pathways such as EphB4 signaling were perturbed. qRT-PCR and immunohistochemistry indicated that several key molecules such as Osteopontin/Spp1, Hmox1, Mmp12, and ERBB2 were markedly altered and/or localized in the preneoplastic lesions, suggesting their participation in the induction of lung cancer. Our findings support a scenario of inflammation-induced carcinogenesis and contribute to a better understanding of the molecular mechanism of MWCNT carcinogenicity. To investigate the chronic effect of the multiwalled carbon nanotube to lungs, we repeatedly administered MWNT-7 to male F344 rats for 2 years. Throuh the experiment, we harvested rat lungs from vehicle control group and MWCNT-treated group at 6 months (Year 0.5), 1 year (Year 1), and 2 years (Year 2) after the begenning of the experiment (3 rats per time point per group). We then performed comparative gene expression profiling analyses for MWCNT-treated vs vehicle control at each time point.