Toxoplasma TgCtwh3 Δrop16 Ⅰ/Ⅲ accelerates neuronal apoptosis and APP production in mouse with acute infection.

OBJECTIVE

To explore the mechanism by which rop16 Ⅰ/Ⅲ -deficient/gra15 Ⅱ -dominant toxoplasma gondii Chinese 1 genotype Wh3 (TgCtwh3 Δrop16 Ⅰ/Ⅲ ) strain induced neuron apoptosis, APP and BACE1 production in vivo and vitro.

METHOD: BALB/c mice were infected by intraperitoneal injection with TgCtwh3 wild type (TgCtwh3 WT) and TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites, respectively. One week after infection, the morphology and number of hippocampal neurons were examined by hematoxylin-eosin (H&E) and Nissl staining. Expression levels of apoptosis-related proteins, APP, BACE1 as well as inflammatory factors proteins and genes in the hippocampus were evaluated using western blotting and qRT-PCR. The hippocampal neuron cell line HT22 was infected with TgCtwh3 WT and TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoite, respectively, and the expression of target proteins was analyzed through immunofluorescence staining and western blotting. Furthermore, HT22 apoptosis was assessed using flow cytometry.

RESULT: BALB/c mice injected with TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites presented abnormal appearance and posture changes as well as declined vitality. The hippocampus assay demonstrated that TgCtwh3 Δrop16 Ⅰ/Ⅲ toxoplasma caused neuron loss, neuron alignment disorder, neuronal nucleus abnormal deep-stained and neuron apoptosis. Furthermore, TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites caused obvious production of APP, BACE1and expression increase of pro-inflammatory factors in hippocampal tissue compared to these in mice infected with TgCtwh3 WT tachyzoites. Contrarily, the expression of transforming growth factor beta 1 (TGF-β1), a pivotal anti-inflammatory cytokine was significantly decreased in TgCtwh3 Δrop16 Ⅰ/Ⅲ infected mice. Further study showed that TgCtwh3 Δrop16 Ⅰ/Ⅲ tachyzoites induced HT22 apoptosis through triggering ERS, meanwhile promoted HT22 to produce APP, BACE1 by activating NF-κB signaling pathway.

CONCLUSION

Our results indicated that the GRA15Ⅱ effector may play a crucial part in neuron apoptosis, pro-inflammatory factors secretion, and APP, BACE1 production. Inversely, ROP16Ⅰ/Ⅲ effector may play a potentially protective role in this process.