Effects of immunological challenge induced by lipopolysaccharide on skeletal muscle fiber type conversion of piglets.

The objective of this study was to investigate the effects of immunological challenge on the skeletal muscle fiber type conversion of piglets. Sixteen Large White weaned barrows (28 ± 3 d, 8.22 ± 0.89 kg BW) were allotted by weight and litter to 2 groups: the control group and the lipopolysaccharide (LPS) group. Saline (control) or LPS was injected intravenously via a jugular catheter on d 1, 3, 5, 7, 9, 11, 13, and 15 at an initial dosage of 80 μg/kg BW, which was increased by 30% at each subsequent injection. Blood samples were collected via the jugular catheter 3 h after the LPS challenge on d -1, 1, 5, 9, and 13. Muscle tissue samples were collected from the LM after exsanguination on d 15. The LPS challenge increased the plasma IL-6, tumor necrosis factor-α (TNF-α), cortisol, IL-1β, and haptoglobin concentrations on d 1 and 5 (P < 0.01) and increased the plasma IL-6 (P < 0.05), TNF-α (P < 0.05), and haptoglobin (P < 0.01) levels on d 9. Compared with that of the control group, the ADG of the LPS group decreased by 40.00% (P < 0.01), 29.52% (P < 0.05), and 19.30% (P < 0.05), and the ADFI decreased by 25.09% (P < 0.01), 23.15% (P < 0.05), and 19.47% (P < 0.05) during d 1 to 4, d 5 to 8, and d 9 to 15, respectively. In the LM of LPS-challenged piglets, myosin heavy chain 1 (MyHC1) mRNA and protein expression tended to be reduced (P = 0.08, 0.09), whereas MyHC2x mRNA, MyHC2b mRNA, and MyHC2 protein expression increased (P < 0.05). The LPS challenge reduced succinic dehydrogenase (SDH) activity (P < 0.05) and increased lactate dehydrogenase (LDH) activity (P < 0.05) in the LM of piglets. Compared with those in the control group, transcriptional peroxisome proliferatoractivated receptor coactivator-α (PGC-α) mRNA (P < 0.05), calcineurin (CaN) mRNA, and protein expression were reduced (P < 0.05), and PGC-α protein expression tended to be reduced (P = 0.08) in the LM of LPS-challenged piglets. These results show that immunological challenge induced by LPS resulted in a shift from type I to type II fibers in the LM of piglets, which may be mediated by the downregulation of the CaN/PGC-a signaling pathway. [ABSTRACT FROM AUTHOR]