Organophosphorus flame retardant TDCPP induces neurotoxicity via mitophagy-related ferroptosis in vivo and in vitro

Tris (1,3-dichloro-2-propyl) phosphate (TDCPP) has neurotoxicity, but its mechanism remains unclear. Evidence recently showed that ferroptosis might be associated with TDCPP-induced neurotoxicity. To explore the role and underlying mechanism of ferroptosis in TDCPP-induced neurotoxicity, the occurrence of ferroptosis was examined in mice and PC12 cells upon TDCPP exposure. The mechanism of TDCPP-induced ferroptosis was clarified in vitro combined with the RNA sequencing assay. The in vivo results showed that orally TDCPP exposure (100 mg/kg, 30 d) inhibited the learning and memory ability of mice, reduced hippocampus neurons, induced malondialdehyde (MDA) accumulation, and decreased glutathione (GSH) and superoxide dismutase (SOD) levels in the hippocampus. Moreover, TDCPP exposure (100 mg/kg, 30 d) altered the ferroptosis and autophagy-related protein abundances in the hippocampus. The in vitro results showed that TDCPP exposure (0, 5, 20, 50, 100, and 200 μM) for 24 h induced dose-dependent cell death in PC12 cells, and the cell death was ameliorated by the co-treatment with ferrostatin-1 (1 μM, 24 h). Similarly, TDCPP exposure (0, 50, 100, and 200 μM) for 24 h increased the levels of MDA and LPO, but decreased the reduced GSH in PC12 cells. Furthermore, TDCPP exposure (0, 50, 100, and 200 μM) for 24 h altered the ferroptosis and autophagy-related protein abundances in PC12 cells. The RNA-sequencing revealed that TDCPP exposure (100 μM, 24 h) induced mitophagy activation in SH-SY5Y cells. Meanwhile, the in vitro experiments confirmed that TDCPP exposure (0, 50, 100, and 200 μM) for 24 h increased abundances of mitophagy-related protein phosphatase and tensin homolog induced kinase 1(PINK1), Parkinson protein 2 E3 ubiquitin-protein ligase (PARKIN), inositol 1,4,5-trisphosphate receptor type 1 (IP3R1), and voltage-dependent anion channel 1 (VDAC1) in PC12 cells. Moreover, TDCPP treatment (100 μM, 24 h) increased the mitochondrial recruitment of PARKIN, decreased the mitochondrial membrane potential (MMP) level, and increased the Fe2+ level in mitochondria. In addition, decreased ATP levels and increased reactive oxygen species (ROS) levels were observed in PC12 cells upon TDCPP exposure (0, 50, 100, and 200 μM) for 24 h. In summary, ferroptosis was associated with TDCPP-induced neurotoxicity, and the mechanism might be related to PINK1/PARKIN-mediated mitophagy initiated by mitochondrial damage.