Mechanistic Insights into Eimeria tenella-Induced Host Cell Apoptosis Through Modulation of the Mitochondrial Permeability Transition Pore

Coccidiosis due to <i>Eimeria tenella</i> remains a major constraint on the poultry industry. Previous studies have revealed that <i>E. tenella</i> infection triggers apoptosis in host cells. The mitochondrial permeability transition pore (MPTP) plays a pivotal role in the apoptosis and necrosis observed in infected host cells. However, the effect of MPTP opening on mitochondrial apoptotic factors remains unclear. To elucidate the dynamic changes in apoptotic signals during MPTP-mediated apoptosis in host cells infected with <i>E. tenella</i>, we established a chicken embryo caecal epithelial cell infection model. Cyclosporin A (CsA) was used to inhibit the MPTP. The infection rate was assessed by Hematoxylin and eosin (H&E) staining, whereas MPTP opening and the abundances of the mitochondrial apoptotic factors Smac, Endo G, and AIF were determined by flow cytometry and ELISA, respectively. The results revealed that both the degree of MPTP opening was markedly reduced in the <i>E. tenella+CsA</i> group compared to the <i>E. tenella</i> group (<i>p</i> < 0.05). Between 24 and 120 h post-infection (hpi), the cytoplasmic levels of Smac, Endo G, and AIF were significantly elevated in the <i>E. tenella</i> group compared with the control group (<i>p</i> < 0.05), while their mitochondrial levels were markedly decreased (<i>p</i> < 0.05). In contrast, mitochondrial expression of these factors was restored in the <i>E. tenella+CsA</i> group (<i>p</i> < 0.05), accompanied by a reduction in their cytoplasmic abundance (<i>p</i> < 0.05). These findings indicate that <i>E. tenella</i> promotes MPTP-dependent release of mitochondrial pro-apoptotic factors into the cytosol during the mid-to-late stages of infection, whereas pharmacological inhibition of the MPTP limits this redistribution.