Alteration of inflammatory cytokines, energy metabolic regulators, and muscle fiber type in the skeletal muscle of postweaning piglets

This study was conducted to determine the alterations of inflammatory cytokines, energy metabolic regulators, and muscle fiber type in the LM of the piglets postweaning. Crossbred piglets (Landrace x Large White) weaned at 14 d age were randomly selected from 8 litters and slaughtered at 0 (W0), 1 (W1), 3 (W3), 5 (W5), or 7 (W7) days postweaning. The glycogen content, free glucose concentration, and enzyme activities, including ATPase (Na+/K+, Ca2+/Mg2+), creatine kinase, and lactic dehydrogenase (LDH), were detected in the skeletal muscle tissue. Concentrations of proinflammatory cytokines, including IL-1 beta, IL-6, and tumor necrosis factor-alpha (TNF-alpha), and anti-inflammatory cytokines, including IL-10 and transforming growth factor-beta 1 (TGF-beta 1), were measured in serum. The mRNA abundance of the above cytokines, energy metabolic regulators, and muscle fiber type related genes were determined via real-time quantitative PCR analysis. The adenosine monophosphate-activated protein kinase alpha (AMPK alpha) signaling was measured by Western blot analysis. Our results showed ATPase activities were lower on W7 d but LDH activity was higher on W3 d after weaning (P < 0.05). Serum TNF-alpha concentration was markedly increased on W1 d, then returned to the value of preweaning (P < 0.05), and almost all the values of inflammatory cytokines were reduced to a low point on W5 d after weaning. Additionally, the IL-6 mRNA abundance was upregulated during W3 to W7 d, but cytokine TNF-alpha was upregulated just on W7 d (P < 0.05). The mRNA abundance of AMPKa and uncoupling protein (UCP) 3 were both higher on W1 and W3 d, and UCP2 was higher on W7 d postweaning (P < 0.05). Myosin heavy chain (MyHC) I and MyHC IIx-type fibers were enhanced on W1 d, then returned to the value of preweaning, and the MyHC IIb-type fiber was significantly increased on W5 and W7 d (P < 0.05). Meanwhile, the value of P-AMPK alpha/T-AMPK alpha increased on W3 d postweaning (P < 0.05) compared with that on W0 d. These results indicate that weaning stress induced inflammation in skeletal muscle tissue during at least 7 d postweaning. It upregulated the expression of proinflammatory cytokines, which then stimulated the AMPK alpha and UCP involved in energy metabolism events, accompanied by significant alterations in muscle fiber type.