Dynamic expression of death receptor adapter proteins tradd and fadd in Eimeria tenella-induced host cell apoptosis

The present study aimed to investigate the dynamic expression patterns of death-receptor adapter proteins TNF-receptor-associated death-domain protein (TRADD) and Fas-associated death-domain protein (FADD) in E. tenella-induced host-cell apoptosis. Culture techniques for primary chick embryo cecum epithelial cells, ELISA, hematoxylin-eosin staining, fluorescence quantitative PCR techniques, and Hoechst-Annexin V-PI apoptosis staining were used to detect the apoptosis rates and dynamic expression patterns of TRADD and FADD in E. tenella host cells at 4, 24, 48, 72, 96, and 120 h. The rates of early apoptosis, late apoptosis, and necrosis of E. tenella- infected group (group T0) were significantly lower (P < 0.05) or highly significantly lower (P < 0.01) than those of control group (group C) at 4 h, but higher (P < 0.05 or P < 0.01) at varying degrees than those of the same group at 24 to 120 h. Compared with group C, both the mRNA and protein expression levels of TRADD in the group T0 cells increased highly significantly (P < 0.01) at 4 and 24 h, and significantly (P < 0.05) at 48, 72, and 120 h. Compared with the mRNA expression in the group C cells, that of TRADD in the group T0 cells increased significantly (P < 0.05) at 96 h. Both the mRNA and protein expression of FADD in the group T0 cells displayed no significant difference (P > 0.05) from those in the group C cells at 4 h. However, FADD expression in the group T0 cells were significantly (P < 0.05) or highly significantly higher (P < 0.01) than those in the group C cells at 24 to 120 h. These observations indicate that in the early developmental stages of E. tenella, the host-cell apoptosis rate decreased, and TRADD expression increased. In the middle and later developmental stages of E. tenella, the host-cell apoptosis rate increased and expression of TRADD and FADD increased. The variation trends of TRADD and FADD expression were significantly positively correlated with the change rule of the host-cell apoptosis rate, respectively. These results indicate that TRADD and FADD may play an important role in E. tenella-induced host-cell apoptosis.