Titanium Dioxide Nanoparticles Induce Cell Cycle Arrest and Apoptosis through Inhibiting PI3K/AKT/mTOR Pathway in Spermatogonia

Titanium dioxide nanoparticles (TiO 2 NPs) can result in the reduction of sperm numbers, but the mechanisms have not been well elucidated. The purpose of this study was to investigate the effects of TiO 2 NPs on cell cycle and apoptosis in spermatogonia and to explore the role of PI3K/AKT/mTOR signaling pathway in this process. The mouse spermatogonia cell line (GC-1) was treated with TiO 2 NPs at different concentrations (0, 25, 50, 75 and 100 μg/mL) for 24 h to detect cell viability, cell cycle, apoptosis, and key proteins related to cell cycle and PI3K/AKT/mTOR signaling pathway. The agonist (IGF-1) and inhibitor (LY294002) of PI3K were used to verify the role of PI3K/AKT/mTOR signaling pathway in cell cycle and apoptosis. TiO 2 NPs significantly inhibited cell proliferation, induced cell cycle arrest at G0/G1 phase and resulted in apoptosis. TiO 2 NPs downregulated the levels of cyclin-dependent kinases (CDKs) and cyclins, including CDK4, CDK2, Cyclin D1 and Cyclin E1, while upregulated the levels of p21 and p53 proteins. Furthermore, TiO 2 NPs inhibited the PI3K/AKT/mTOR signaling pathway by decreasing the levels of p-PI3K, p-AKT and p-mTOR. IGF-1 reversed the G0/G1 phase arrest and apoptosis caused by TiO 2 NPs. However, LY294002 aggravated the G0/G1 phase arrest and apoptosis resulting from TiO 2 NPs. Collectively, TiO 2 NPs induced cell cycle arrest at G0/G1 phase and apoptosis through inhibiting the activation of PI3K/AKT/mTOR pathway, which could be the main reason for the reduction in sperm numbers caused by TiO 2 NPs.