Synergistic Effect of ROS and p38 MAPK in Apoptosis of TM4 Cells Induced by Titanium Dioxide Nanoparticles

The adverse effects of titanium dioxide nanoparticles (TiO₂ NPs) on the integrity of the blood-testis barrier (BTB) are widely recognized. However, the underlying mechanisms remain incompletely understood. The integrity of the BTB is imperative for the preservation of male reproductive health. TM4 cells, which are major component of the BTB, play a critical role in its integrity. The apoptosis of TM4 cells is closely associated with the disruption of the BTB. Therefore, we selected TM4 cells as experimental models to investigate the apoptosis induced by TiO₂ NPs and the underlying mechanisms. Cell viability, excessive production of reactive oxygen species (ROS), activation of p38 mitogen-activated protein kinase (MAPK) pathway, and apoptosis-related protein expression levels were determined under various concentrations (50, 100, 150, and 200 μg/mL) of TiO₂ NPs exposure. The results indicate that TiO₂ NPs induced the overproduction of ROS and activated the p38 MAPK signaling pathway, which subsequently led to apoptosis. The ROS scavenger N-acetylcysteine (NAC) was able to suppress the activation of p38 MAPK pathway induced by TiO₂ NPs, while the p38 MAPK inhibitor SB203580 mitigated TiO₂ NPs-induced ROS overproduction and subsequent apoptosis, suggesting an interplay between ROS overproduction and p38 MAPK pathway activation. In summary, TiO₂ NPs induced mitochondrial apoptosis via the ROS-p38 MAPK axis. A positive feedback regulatory mechanism exists between the two processes, promoting apoptosis in TM4 cells through a synergistic effect.