Toxoplasma TgCtwh3 Δ rop16 Ⅰ/Ⅲ accelerates neuronal apoptosis and APP production in mouse with acute infection

Abstract

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 GRA15_Ⅱ effector may play a crucial part in neuron apoptosis, pro-inflammatory factors secretion, and APP, BACE1 production. Inversely, ROP16_Ⅰ/Ⅲ effector may play a potentially protective role in this process.

Keywords: APP; Apoptosis; Hippocampal neuron; ROP16Ⅰ/Ⅲ; T.gondii Chinese 1 genotype Wh3 strain.

Fig. 1

TgCtwh3 acute infection mice model was established.

Fig. 2

Hippocampal neuron apoptosis was caused by TgCtwh3 Δrop16_Ⅰ/Ⅲ infection.

Fig. 3

TgCtwh3 Δrop16_Ⅰ/Ⅲ infection increased mouse hippocampal tissue APP, BACE1 expression.

Fig. 4

Pro-inflammatory cytokines secretion was induced in mouse hippocampus by TgCtwh3 Δrop16_Ⅰ/Ⅲ infection.

Fig. 5

HT22 apoptosis was caused by TgCtwh3 Δrop16_Ⅰ/Ⅲ infection.

Fig. 6

Expression of APP and BACE1 in HT22 was directly facilitated by TgCtwh3 Δrop16_Ⅰ/Ⅲ.

Fig. 7

HT22 apoptosis was promoted by TgCtwh3 Δrop16_Ⅰ/Ⅲ through ERS pathway.

Fig. 8

APP and BACE1 expression were elevated in HT22 by TgCtwh3 Δrop16_Ⅰ/Ⅲ through promoting NF-κB signaling.

Fig. 9

Mechanism with which TgCtwh3 Δrop16_Ⅰ/Ⅲ tachyzoite induces neuron apoptosis and APP production in mouse with acute infection at the cellular and molecular level in our experiments.