Abstract: In order to investigate the effects of lipopolysaccharide (LPS) on the mitochondrial signaling pathway in muscle cells of Tan sheep, M longissimus dorsi muscles from six-month-old Tan sheep were aged at 4 ℃ for 0, 6, 12, 24 and 72 h postmortem and evaluated for pH, ATP content, cell apoptosis rate, cell apoptosis-related enzyme activity, succinatedehydrogenase (SDH) activity, citrate synthase (CS) activity, B-cell lymphoma 2 (Bcl-2) family protein contents, and cytochrome c (Cyt-c) and cysteinyl aspartate specific proteinase 3 (Caspase-3) expression levels. The results showed that the apoptosis rate and Bcl-2-associated X protein (Bax)/Bcl-2 ratio in the control and LPS-induced groups were significantly increased during postmortem aging (P < 0.05). The activities of Caspase-3 and Caspase-9 increased first and then decreased. After LPS treatment, the activities of Caspase-3 and Caspase-9 were higher than those in the control group at all time points. The pH, Cyt-c reduction level and mitochondrial ATP content were significantly decreased overall (P < 0.05). The relative expression level of Cyt-c was significantly increased in both groups at 12 h postmortem, and decreased during 24–72 h in the LPS group. The content of Caspase-3 activated fragment protein in the LPS treatment group was higher than that in control group at the same time points. In conclusion, LPS could activate Caspase-3 and Caspase-9, and reduce the mitochondrial content of ATP and consequently energy metabolism level, thus affecting the activities of SDH and CS, promoting the release of Cyt-C, and increasing Bax/Bcl-2 ratio, and finally inducing cell apoptosis through the mitochondrial signaling pathway.

Key words: Tan sheep; lipopolysaccharide; cell apoptosis; mitochondrial signaling pathway