Dissociation of AMP-activated protein kinase and p38 mitogen-activated protein kinase signaling in skeletal muscle

AMP-activated protein kinase (AMPK) is widely recognized as an important regulator of glucose transport in skeletal muscle. The p38 mitogen-activated protein kinase (MAPK) has been proposed to be a component of AMPK-mediated signaling. Here we used several different models of altered AMPK activity to determine whether p38 MAPK is a downstream intermediate of AMPK-mediated signaling in skeletal muscle. First, L6 myoblasts and myotubes were treated with AICAR, an AMPK stimulator. AMPK phosphorylation was significantly increased, but there was no change in p38 MAPK phosphorylation. Similarly, AICAR incubation of isolated rat extensor digitorum longus (EDL) muscles did not increase p38 phosphorylation. Next, we used transgenic mice expressing an inactive form of the AMPKα2 catalytic subunit in skeletal muscle (AMPKα2i TG mice). AMPKα2i TG mice did not exhibit any defect in basal or contraction-induced p38 MAPK phosphorylation. We also used transgenic mice expressing an activating mutation in the AMPKγ1 subunit (γ1R70Q TG mice). Despite activated AMPK, basal p38 MAPK phosphorylation was not different between wild type and γ1R70Q TG mice. In addition, muscle contraction-induced p38 MAPK phosphorylation was significantly blunted in the γ1R70Q TG mice. In conclusion, increasing AMPK activity by AICAR and AMPKγ1 mutation does not increase p38 MAPK phosphorylation in skeletal muscle. Furthermore, AMPKα2i TG mice lacking contraction-stimulated AMPK activity have normal p38 MAPK phosphorylation. These results suggest that p38 MAPK is not a downstream component of AMPK-mediated signaling in skeletal muscle.