Shelterin differentially respond to oxidative stress induced by TiO2-NPs and regulate telomere length in human hepatocytes and hepatocarcinoma cells in vitro

Titanium dioxide nanoparticles (TiO2-NPs) have raised serious attention for their widely use and potential adverse effects on human mainly due to producing ROS. However, the influence of TiO2-NPs on telomere maintaining has not been studied clearly. Shelterin plays core roles in telomere length (TL) regulation. Abnormal TL are associated with chromosome instability (CIN) and high risk of diseases. This study investigated whether TiO2-NPs affect TL to induce CIN through ROS generation and the possible mechanisms. Human hepatocyte L-02 and hepatocarcinoma cells QGY were exposed to TiO2-NPs (0, 40, 80 μg/mL) for 72 h. The intracellular hydrogen dioxide (H2O2) concentration were measured. The TL, Nrf-2, and three core shelterin components (TRF1, TRF2, and POT1) transcription level were determined by quantitative real-time PCR. CIN was measured by cytokinesis-block micronucleus assay. TiO2-NPs exposure increased intracellular H2O2 in both L-02 and QGY cells, and induced Nrf-2, TRF1, TRF2, POT1 downregulated transcription compared with control (P < 0.001) in L-02 but all upregulated (P < 0.05) in QGY. Significant TL shortening (P < 0.001) and CIN increase (P < 0.01) in L-02 cells were observed but not in QGY cells. The differentially responses of the tested components of shelterin and Nrf-2 to oxidative stress induced by TiO2-NPs led to the weakened telomere protection in normal cells and effective telomere maintenance in cancer cells, respectively. The upregulation of Nrf-2 and shelterin could protect TL and chromosome stability against TiO2-NPs exposure.