5'-AMP activated protein kinase [alpha]2 controls substrate metabolism during post-exercise recovery via regulation of pyruvate dehydrogenase kinase 4

Key points There is lower fat oxidation during post-exercise recovery in mice lacking 5'-AMP activated protein kinase [alpha]2 (AMPK[alpha]2). AMPK[alpha]2 is involved in post-transcriptional and not transcriptional regulation of pyruvate dehydrogenase kinase 4 (PDK4) in muscle. Exercise-induced AMPK[alpha]2 activity increases PDK4 protein content, in turn inhibiting pyruvate dehydrogenase activity and glucose oxidation. The mechanism for increased post-exercise fat oxidation is by inhibition of carbohydrate oxidation allowing increased fat oxidation rather than by direct stimulation of fat oxidation. It is well known that exercise has a major impact on substrate metabolism for many hours after exercise. However, the regulatory mechanisms increasing lipid oxidation and facilitating glycogen resynthesis in the post-exercise period are unknown. To address this, substrate oxidation was measured after prolonged exercise and during the following 6 h post-exercise in 5´-AMP activated protein kinase (AMPK) [alpha]2 and [alpha]1 knock-out (KO) and wild-type (WT) mice with free access to food. Substrate oxidation was similar during exercise at the same relative intensity between genotypes. During post-exercise recovery, a lower lipid oxidation (P < 0.05) and higher glucose oxidation were observed in AMPK[alpha]2 KO (respiratory exchange ratio (RER) = 0.84 ± 0.02) than in WT and AMPK[alpha]1 KO (average RER = 0.80 ± 0.01) without genotype differences in muscle malonyl-CoA or free-carnitine concentrations. A similar increase in muscle pyruvate dehydrogenase kinase 4 (PDK4) mRNA expression in WT and AMPK[alpha]2 KO was observed following exercise, which is consistent with AMPK[alpha]2 deficiency not affecting the exercise-induced activation of the PDK4 transcriptional regulators HDAC4 and SIRT1. Interestingly, PDK4 protein content increased (63%, P < 0.001) in WT but remained unchanged in AMPK[alpha]2 KO. In accordance with the lack of increase in PDK4 protein content, lower (P < 0.01) inhibitory pyruvate dehydrogenase (PDH)-E1[alpha] Ser293 phosphorylation was observed in AMPK[alpha]2 KO muscle compared to WT. These findings indicate that AMPK[alpha]2 regulates muscle metabolism post-exercise through inhibition of the PDH complex and hence glucose oxidation, subsequently creating conditions for increased fatty acid oxidation.