Effects Of Immunological Stress On Skeletal Muscle Fiber Type Of Piglets And Its Mechanism Preliminarily

Muscle fibers directly affect the intramuscular fat content, tenderness, and meat quality. In the animal primary stage, immune stress are easily happened at this stage. Immune stress make the inflammatory cytokine rises sharply, such as TNF-α. In vitro studies, TNF-α decreased MyHC1 mRNA expression, while increased MyHC2 m RNA expression in C2C12 cells. We speculate that immune stress may regulate the expression of muscle fibers type by TNF-α. To verify the above hypoyhesis, this thesis has carried out the following research, which can provide the theoretical foundation for regulating immune stress, improves the production performance of piglets and for improving the pork quality. 1、 Effects of immune stress on skeletal muscle fiber type transition of piglets16 weaned piglets was selected, and randomly divided into control group and LPS group. saline or Lipopolysaccharide(LPS) were performed intravenously via the catheter at 48 h intervals, at an initial dosage of 80μg/kg.BW, increased by 30% at each following injections, the experiment lasted for 15 d. The result showed that, On d 9, the concentrations of plasma IL-6, TNF-α and haptoglobin of LPS-treated piglets were higher than that of the control group(P <0.05), which suggested that piglets were in chronic immune stress. In muscle, MyHC1 mRNA and protein expression signif icantly reduced(P<0.05), MyHC2 b m RNA and My HC2 protein expression signif icantly increased( P<0.05), the CaN, PGC-α expression significantly reduced(P<0.05), the activity of oxidase enzyme in LM decreased signif icantly(P<0.05), the activity of glycolysis enzyme increased significantly(P<0.05), suggesting that increasing injection of LPS induced chronic immune stress in piglets, which resulted in the shift from fibers of typeⅠto typeⅡin LM. 2、Using the model of rat to explore the effect of TNF-α on skeletal muscle fiber type transition and its mechanism72 weaned SD male rats of 4 weeks were selected, then randomly divided into groups, control group, LPS group and monoclonal antibody group respectively(LPS+TNF-α monoclonal antibody group). LPS group and monoclonal antibody group intraperitoneal injection LPS in 1, 3, 5, 7 d, at an initial dosage of 1 mg/kg.BW, increased by 30% at each following injections. Control group injected corresponding dose of saline, monoclonal antibody groups injected 2 mg/kg. Intraperitoneal injection Infliximab before injecting LPS 1 h. After that, do nothing for 4 weeks. The result showed that, increasing injection of LPS lead to elevate levels of inflammatory cytokines in serum of rats, reduce the expression of CaN and PGC-α level at the same time, meanwhile resulted in the shift from fibers of typeⅠto typeⅡin LM. By using monoclonal antibody reduced the level of TNF-α, and alleviated the skeletal muscle fiber type conversion., suggesting that muscle fiber type transform associated with TNF-α elevated. Stop the injection of LPS, relative expression quantity of My HC w ere no signif icant difference, which suggested that stop the immune stress, the influence of the immune stress on skeletal muscle fiber type gradually eliminated. 3、Using cell to explore mechanism of TNF-α on skeletal muscle fiber type transitionUsing 10% fetal bovine serum growth medium cultured C2C12 cells, then vaccinated in 96 well plates and 6 well plate. Waiting for the 80% fusion, 2% inactivated horse serum differentiation medium replaced the growth medium. After differentiation for 3d, different concentrations of TNF-α(0 ng/mL, 5 ng/mL, 10 ng/mL, 20 ng/mL) added into the culture medium, then cultured 3d. Each increment has three repeats. The study showed that, TNF-α significantly reduced MyHC1 m RNA expression level, TNF-α signif icantly increased the ratio of MyHC2b/My HC1, which showed that TNF-α resulted in the shift from fibers of typeⅠto typeⅡin C2C12, and signif icantly reduced intracellular Ca2+ concentration(P < 0.05), indicating that the immune stress resulted in the shift from fibers of typeⅠto typeⅡin LM, which may be mediated by CaN/PGC-α signaling pathway.In conclusion, repeated injection of LPS, increased by 30% at each following injections, successfully induced a chronic immune stress in piglets. immune stress resulted in the shift from fibers of typeⅠto typeⅡ in LM of piglets, which may be through CaN/ PGC-α signaling pathway.