Effects of α-AMPK knockout on exercise-induced gene activation in mouse skeletal muscle

We tested the hypothesis that 5'AMP-activated protein kinase (AMPK) plays an important role in regulating the acute, exercise-induced activation of metabolic genes in skeletal muscle, which were dissected from whole-body alpha 2- and alpha 1-AMPK knockout (KO) and wild-type (WT) mice at rest, after treadmill running (90 min), and in recovery. Running increased alpha 1-AMPK kinase activity, phosphorylation (P) of AMPK, and acetyl-CoA carboxylase (ACC)beta in alpha 2-WT and alpha 2-KO muscles and increased alpha 2-AMPK kinase activity in alpha 2-WT. In alpha 2-KO muscles, AMPK-P and ACC beta-P were markedly lower compared with alpha 2-WT. However, in alpha 1-WT and alpha 1-KO muscles, AMPK-P and ACC beta-P levels were identical at rest and increased similarly during exercise in the two genotypes. The alpha 2-KO decreased peroxisome-proliferator-activated receptor 7 coactivator (PGC)-1 alpha, uncoupling protein-3 (UCP3), and hexokinase II (HKII) transcription at rest but did not affect exercise-induced transcription. Exercise increased the mRNA content of PGC-1 alpha, Forkhead box class O (FOXO)1, HKII, and pyruvate dehydrogenase kinase 4 (PDK4) similarly in alpha 2-WT and alpha 2-KO mice, whereas glucose transporter GLUT 4, carnitine palmitoyltransferase I (CPTI), lipoprotein lipase, and UCP3 mRNA were unchanged by exercise in both genotypes. CPTI mRNA was lower in alpha 2-KO muscles than in alpha 2-WT muscles at all time-points. In alpha 1-WT and alpha 1-KO muscles, running increased the mRNA content of PGC-1 alpha and FOXO1 similarly. The alpha 2-KO was associated with lower muscle adenosine 5'-triphosphate content, and the inosine monophosphate content increased substantially at the end of exercise only in alpha 2-KO muscles. In addition, subcutaneous injection of 5-aminoimidazole-4-carboxamide-1-beta-4-ribofuranoside (AICAR) increased the mRNA content of PGC-1 alpha, HKII, FOXO1, PDK4, and UCP3, and alpha 2-KO abolished the AICAR-induced increases in PGC-1 alpha and HKII mRNA. In conclusion, KO of the alpha 2- but not the alpha 1-AMPK isoform markedly diminished AMPK activation during running. Nevertheless, exercise-induced activation of the investigated genes in mouse skeletal muscle was not impaired in alpha- or alpha 2-AMPK KO muscles. Although it cannot be ruled out that activation of the remaining alpha-isoform is sufficient to increase gene activation during exercise, the present data do not support an essential role of AMPK in regulating exercise-induced gene activation in skeletal muscle.