cGAS-STING pathway mediates TiO2 nanoparticle-induced TM4 cell apoptosis via MCUb downregulation and calcium overload.

Titanium dioxide nanoparticles (TiO2 NPs) pose potential reproductive toxicity risks, notably compromising the blood-testis barrier (BTB), for which Sertoli cells are pivotal in maintaining integrity. However, certain research gaps remain regarding the molecular mechanisms by which TiO2 NPs induce apoptosis in Sertoli cells. This study aims to investigate whether TiO2 NPs trigger apoptosis through cGAS-STING-mediated down-regulation of MCUb in mouse Sertoli (TM4) cells. TM4 cells were exposed to various concentrations of TiO2 NPs (0, 25, 50, 75 and 100 μg/mL) for different periods (0, 3, 6, 12 and 24 h). Exposure to TiO2 NPs generated excessive reactive oxygen species (ROS), caused DNA damage, up-regulated cGAS, STING and TBK1 expression, down-regulated MCUb expression, elevated Ca2+ levels in cytoplasm and mitochondria, and enhanced apoptosis in TM4 cells, with statistical significance observed from 50 μg/mL onward. A time-dependent biphasic regulation of STING was observed. The ROS scavenger N-acetyl-L-cysteine (NAC) prevented DNA damage and cGAS-STING activation, while the STING inhibitor C176 restored MCUb expression, normalized Ca2+ levels and reduced apoptosis. Exposure to TiO2 NPs induces an excessive production of ROS, leading to DNA damage, which subsequently influences the expression of the MCUb protein via the cGAS-STING signaling pathway, ultimately causing Ca2+ overload and triggering mitochondrial apoptosis in TM4 cells. These findings elucidate a novel molecular mechanism by which TiO2 NPs induce apoptosis in TM4 cells and provide insights for the prevention of BTB disruption.