AMPKα stimulates skeletal muscle fatty acid utilization during in vivo exercise in mice

Existing controversy regarding the importance of AMP-activated protein kinase (AMPK) in fatty acid (FA) oxidation in skeletal muscle with contraction/exercise may to some extent pertain to redundant AMPKα1 signaling. Using a mouse model lacking both AMPKα1 and -α2 in skeletal muscle specifically (mdKO) we hypothesized that FA utilization would be impaired in skeletal muscle. Calorimetric analysis showed a similar respiratory exchange ratio (RER) of AMPKα WT and mdKO mice when fed normal chow, a high fat diet or with prolonged fasting. Though, in vivo treadmill exercise at the same relative intensity induced a higher RER in mdKO mice compared to WT (WT=0.81; mdKO=0.87; p<0.01) indicating a decreased utilization of FA. Ex vivo incubation of soleus muscle revealed that basal and contraction-induced FA oxidation was impaired in mdKO mice, suggesting that the increased RER during in vivo running exercise originated from decreased skeletal muscle FA oxidation. A decreased muscle protein expression of CD36 and FABPpm (by 17-40%) together with abolishment of TBC1D1 Ser237 phosphorylation in mdKO mice, may result in lower FA transport capacity and FA transport protein translocation to sarcolemma, respectively. In summary this study shows that the catalytically active AMPKα subunits are required for normal stimulation of FA utilization during exercise and contractions. Four wild type and 3 AMPKα1α2 double knockout mice were used.