Irreversible disruption of the cytoskeleton as induced by non-cytotoxic exposure to titanium dioxide nanoparticles in lung epithelial cells

Exposure to TiO2 NPs induces several cellular alterations after NPs uptake including disruption of cytoskeleton that is crucial for lung physiology but is not considered as a footprint of cell damage. We aimed to investigate cytoskeleton disturbances and the impact on cell migration induced by an acute TiO2 NPs exposure (24 h) and the recovery capability after 6 days of NPs-free treatment, which allowed investigating if cytoskeleton damage was reversible. Exposure to TiO2 NPs (10 mu g/cm(2)) for 24 h induced a decrease 20.2% and 25.1% in tubulin and actin polymerization. Exposure to TiO2 NPs (10 mu g/cm(2)) for 24 h followed by 6 days of NPs-free had a decrease of 26.6% and 21.3% in tubulin and actin polymerization, respectively. The sustained exposure for 7 days to 1 mu g/cm(2) and 10 mu g/cm(2) induced a decrease of 22.4% and 30.7% of tubulin polymerization respectively, and 28.7% and 46.2% in actin polymerization. In addition, 24 h followed 6 days of NPs-free exposure of TiO2 NPs (1 mu g/cm(2) and 10 mu g/cm(2)) decreased cell migration 40.7% and 59.2%, respectively. Cells exposed (10 mu g/cm(2)) for 7 days had a decrease of 65.5% in cell migration. Ki67, protein surfactant B (SFTPB) and matrix metalloprotease 2 (MMP2) were analyzed as genes related to lung epithelial function. The results showed a 20% of Ki67 upregulation in cells exposed for 24 h to 10 mu g/cm(2) TiO2 NPs while a downregulation of 20% and 25.8% in cells exposed to 1 mu g/cm(2) and 10 mu g/cm(2) for 24 h followed by 6 days of NPs-free exposure. Exposure to 1 mu g/cm(2) and 10 mu g/cm(2) for 24 h and 7 days upregulates SFTPB expression in 53% and 59% respectively, MMP2 expression remain unchanged. In conclusion, exposure of TiO2 NPs affected cytoskeleton of lung epithelial cells irreversibly but this damage was not cumulative.