Role of the AMPKgamma3 Isoform in Hypoxia-stimulated Glucose Transport in Glycolytic Skeletal Muscle

Skeletal muscle glucose transport is regulated via the canonical insulin-signaling cascade as well as by energy-sensing signals. 5'-AMP-activated protein kinase (AMPK) has been implicated in the energy status regulation of glucose transport. We determined the role of the AMPKgamma3 isoform in hypoxia-mediated energy status signaling and glucose transport in fast-twitch glycolytic extensor digitorum longus (EDL) muscle from AMPKgamma3-knockout (KO) mice and wild-type mice. Although hypoxia increased glucose transport (P < 0.001) in wild-type mice, this effect was attenuated in AMPKgamma3-KO mice (45% reduction, P < 0.01). The role of Ca(2+)-mediated signaling was tested using the Ca(2+)/calmodulin competitive inhibitor KN-93. KN-93 exposure reduced hypoxia-mediated glucose transport in AMPKgamma3-KO and wild-type mice (P < 0.05). To further explore the underlying signaling mechanisms, phosphorylation of CaMKII, AMPK, ACC, and TBC1D1/D4 as well as isoform-specific AMPK activity was determined. Basal and hypoxia-mediated phosphorylation of CaMKII, AMPK, and ACC as well as alpha1- and alpha2-associated AMPK activity was comparable between AMPKgamma3-KO and wild-type mice. KN-93 reduced hypoxia-mediated CaMKII phosphorylation in AMPKgamma3-KO and wild-type mice (P < 0.05), whereas phosphorylation of AMPK and ACC as well as alpha1- and alpha2-associated AMPK activity was unaltered. Hypoxia increased TBC1D1/D4 phosphorylation in AMPKgamma3-KO and wild-type mice (P < 0.001). KN-93 exposure prevented this effect in AMPKgamma3-KO, but not in wild-type mice. Taken together, we provide direct evidence for a role of the AMPKgamma3 isoform in hypoxia-mediated glucose transport in glycolytic muscle. Moreover, hypoxia-mediated TBC1D1/D4 phosphorylation was uncoupled from glucose transport in AMPKgamma3-KO mice, indicating that TBC1D1/D4-independent mechanisms contribute to glucose transport in skeletal muscle.