Titanium Dioxide Nanoparticles Induce Mitochondrial Dynamic Imbalance and Damage in HT22 Cells

Mitochondria, as dynamic organelles, are precisely regulated by fusion and fission. The dynamic balance of fusion and fission controls mitochondrial morphology and their subcellular location and function. Exposure to titanium dioxide nanoparticles (TiO2 NPs) may cause serious health problems. However, how TiO2 NPs affect the mitochondrial dynamics remains unclear. In the present study, we investigated the changes of mitochondrial dynamics in the TiO2NPs-treated HT22 cells by confocal and stimulated emission depletion (STED) microscopy. The confocal images demonstrated obvious changes in the average length and density of the mitochondria after TiO2 NPs treatment, while STED images further obtained the nanoscale submitochondrial structures of the mitochondria under TiO2 NPs insult. The fluorescence intensity distributions suggested that mitochondria fragmented in the TiO2 NPs-treated cells. TiO2 NPs treatment caused mitochondrial dynamic imbalance due to the imbalanced expression of dynamin-related protein 1 (Drp1) and optic atrophy 1 (Opa1). Furthermore, we examined the levels of oxidative stress and mitochondrial membrane potential (MMP) and the generation of adenosine triphosphate (ATP), which revealed the damage of mitochondria under TiO2 NPs exposure. Meanwhile, the significant changes of expressions of B-cell lymphoma 2-associated X protein (Bax), B-cell lymphoma 2 (Bcl-2), cytochrome c (Cyt C), and caspase 9 demonstrated that TiO2 NPs treatment activated the mitochondrial-related apoptosis pathway. These cellular events can be largely prevented via cell incubation with mitoTEMPO, a mitochondria-targeted superoxide scavenger. Our results confirm that TiO2 NPs targeted the mitochondria, inducing mitochondrial dynamic imbalance and damage in HT22 cells. Our study provides an insightful understanding of the mechanisms underlying TiO2 NPs cytotoxicity.