Toxoplasma gondii protects against H2O2-induced apoptosis in ARPE-19 cells through the transcriptional regulation of apoptotic elements and downregulation of the p38 MAPK pathway

Purpose: Toxoplasmosis, which is caused by the protozoan parasite Toxoplasma gondii, can lead to severe visual impairment. T. gondii inhibits or delays programmed cell death caused by various apoptotic triggers; however, the mechanisms involved in the T. gondii-induced suppression of apoptosis in retinal cells have not been analysed in detail. Methods: We investigated the role of T. gondii infection in H2O2-induced apoptosis in human retinal pigment epithelial cells (ARPE-19) by monitoring the activities of apoptosis-regulating molecules and mitogen-activated protein kinases (MAPKs), including p38 MAPK. We also examined the gene downstream from p38 MAPK. Results: T. gondii infection significantly inhibited the cellular toxicity of H2O2 (500 mu m) and increased cell viability in a multiplicity of infection (MOI)-dependent manner by reducing DNA fragmentation and reactive oxygen species (ROS) generation in ARPE-19 cells. Western blot analysis also showed that T. gondii infection prevented the host cell expression of proapoptotic factors, such as Bad and Bax, and the activation of caspase-3. Infection with T. gondii increased the expression of the anti-apoptotic factor Bcl-2 in ARPE-19 cells under oxidative stress. In accordance with these findings, Toxoplasma infection was protective enough to suppress the phosphorylation of p38 MAPK following H2O2 treatment. Exposure to H2O2 increased the expression of heme oxygenase-1 (HO-1) in ARPE-19 cells, and its expression was significantly inhibited in H2O2-treated infected cells. Conclusion: The protective function of T. gondii infection against ROS-induced apoptosis results from changes in the expression of apoptotic molecules and the downregulation of stress-induced intracellular signalling.