title: Role of the AMPKgamma3 isoform in hypoxia-stimulated glucose transport in glycolytic skeletal muscle.
abstract: 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.
authors.affiliation: Department of Molecular Medicine and Surgery, Section for Integrative Physiology, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Atul S
authors.initials: AS
authors.lastname: Deshmukh
authors.forename: Stephan
authors.initials: S
authors.lastname: Glund
authors.forename: Robby Z
authors.initials: RZ
authors.lastname: Tom
authors.forename: Juleen R
authors.initials: JR
authors.lastname: Zierath
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D001596:Benzylamines / Q000494:pharmacology; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology; D005260:Female; D020690:GTPase-Activating Proteins; D005947:Glucose / Q000378:metabolism*; D051246:Glucose Transport Proteins, Facilitative / Q000378:metabolism*; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology; D000096926:Benzenesulfonamides
chemical_list: D055372:AMP-Activated Protein Kinases; D001596:Benzylamines; D002118:Calcium; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D020690:GTPase-Activating Proteins; D005947:Glucose; D051246:Glucose Transport Proteins, Facilitative; D009687:Nuclear Proteins; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; C095906:Tbc1d1 protein, mouse; C072105:KN 93; D000096926:Benzenesulfonamides; C526221:Prkag3 protein, mouse