Sylow, Lykke6; Kleinert, Maximilian6; Pehmøller, Christian7; Prats Gavalda, Clara8; Chiu, Tim T5; Klip, Amira5; Richter, Erik6; Jensen, Thomas Elbenhardt6
1 PhD, Department of Nutrition, Exercise and Sports, Faculty of Science, Københavns Universitet2 Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, Københavns Universitet3 Section of Systems Biology Research, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, Københavns Universitet4 LUKKET: 2012 Undervisningsudvalg, Department of Exercise and Sport Sciences, Faculty of Science, Københavns Universitet5 Program in Cell Biology, The Hospital for Sick Children, Toronto6 Molecular Physiology, Department of Nutrition, Exercise and Sports, Faculty of Science, Københavns Universitet7 LUKKET: 2012 Undervisningsudvalg, Department of Exercise and Sport Sciences, Faculty of Science, Københavns Universitet8 Section of Systems Biology Research, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, Københavns Universitet
Skeletal muscle plays a major role in regulating whole body glucose metabolism. Akt and Rac1 are important regulators of insulin-stimulated glucose uptake in skeletal muscle. However the relative role of each pathway and how they interact is not understood. Here we delineate how Akt and Rac1 pathways signal to increase glucose transport independently of each other and are simultaneously downregulated in insulin resistant muscle. Pharmacological inhibition of Rac1 and Akt signalling was used to determine the contribution of each pathway to insulin-stimulated glucose uptake in mouse muscles. The actin filament-depolymerizing agent LatrunculinB was combined with pharmacological inhibition of Rac1 or Akt, to examine whether either pathway mediates its effect via the actin cytoskeleton. Akt and Rac1 signalling were investigated under each condition, as well as upon Akt2 knockout and in ob/ob mice, to uncover whether Akt and Rac1 signalling are independent and whether they are affected by genetically-induced insulin resistance. While individual inhibition of Rac1 or Akt partially decreased insulin-stimulated glucose transport by ~40% and ~60%, respectively, their simultaneous inhibition completely blocked insulin-stimulated glucose transport. LatrunculinB plus Akt inhibition blocked insulin-stimulated glucose uptake, while LatrunculinB had no additive effect on Rac1 inhibition. In muscles from severely insulin-resistant ob/ob mice, Rac1 and Akt signalling were severely dysregulated and the increment in response to insulin reduced by 100% and 90%, respectively. These findings suggest that Rac1 and Akt regulate insulin-stimulated glucose uptake via distinct parallel pathways, and that insulin-induced Rac1 and Akt signalling are both dysfunctional in insulin resistant muscle. There may thus be multiple treatment targets for improving insulin sensitivity in muscle.
Cellular Signalling, 2014, Vol 26, Issue 2, p. 323-331