Thesis presented February 17, 2016

Abstract:
Titanium dioxide (TiO₂) belongs to the top nanoparticles (NPs) most produced worldwide. This raises the question of their impact on human health, especially through inhalation, which is the main exposure route in occupational settings. It was previously shown in vitro that these NPs induce DNA damage and impair DNA repair activity. The aim here is to study the underlying toxicity mechanisms, in human A549 epithelial alveolar cells exposed to 1-100 µg/ml TiO₂ NPs during 4-48 h. The expression of 40 genes and 6 proteins involved in DNA repair was investigated by RT-qPCR and western-blotting. The impact of TiO₂ NPs on upstream regulators such as the methylation rate of some corresponding gene promoters, proteasome activity and cellular signaling through phosphorylation was assayed as well. Moreover cyto-/geno-toxicity and DNA repair gene expression patterns were compared with those of BEAS-2B bronchial epithelial cells. Results show a global down-regulation of genes and proteins in all DNA repair pathways. This could be partly explained by the down-regulation of transcriptional regulators and increased gene promoter methylation and caspase-like proteasome activity. TiO₂ NPs also scramble the phosphoproteome. While invisible on a global scale, this dysregulation affects numerous proteins involved in diverse cellular processes, which reflect the toxicity pathways reported for these NPs. Although cell proliferation is unaffected, a significant impact is observed on cell cycle, as well as on a few proteins involved in DNA repair. Finally cyto-/geno-toxicity and DNA repair gene expression profiles are similar in both A549 and BEAS-2B cells, thereby strengthening the relevance of using any of these cell lines in nanomaterial genotoxicity studies. On the whole these data bring novel insights into TiO₂-NP toxicity mechanisms, which could especially explain the previously observed impairment of DNA repair activity.

Keywords:
Nanotoxicology, Genotoxicity, Toxicity, Nanoparticle, DNA repair, DNA damage

On-line thesis.