Muscle-specific genetic ablation of p21-activated kinase (PAK)2, but not whole-body PAK1 knockout, impairs glucose tolerance in mice. r Insulin-stimulated glucose uptake partly relies on PAK2 in glycolytic extensor digitorum longus muscle r By contrast to previous reports, PAK1 is dispensable for insulin-stimulated glucose uptake in mouse muscle.

Non-standard abbreviations24 2DG: 2-Deoxyglucose 25 AUC: Area under the curve 26 BCA: Bicinchoninic acid 27 BW: Body weight 28 dKO: Double knockout 29 EDL: Extensor digitorum longus 30 FM: Fat mass 31 GLUT4: Glucose transporter 4 32 GTT: Glucose tolerance test 33 HFD: High-fat diet 34 HOMA-IR: Homeostatic Model Assessment of Insulin Resistance 35 ITT: Insulin tolerance test 36 i.p.: Intraperitoneal 37 KO: Knockout 38 L6-GLUT4myc: Rat L6 skeletal muscle cells overexpressing myc-tagged GLUT4 39 LBM: Lean body mass 40 mKO: Muscle-specific knockout 41 NOX: NADPH oxidase 42 PAK: p21-activated kinase 43 PI3K: Phosphoinositide 3-kinase 44 RER: Respiratory exchange ratio 45 r.o.: Retro-orbital 46 VO 2 : Oxygen uptake 47 48Glucose transport into skeletal muscle is essential for maintaining whole-body glucose homeostasis 49 and accounts for the majority of glucose disposal in response to insulin. The group I p21-activated 50 kinase (PAK) isoforms PAK1 and PAK2 are in skeletal muscle activated in response to insulin and 51 evidence suggests that PAK1 is necessary for insulin-stimulated GLUT4 translocation. In 52 accordance, insulin-induced PAK1 and PAK2 signalling are impaired in insulin-resistant skeletal 53 muscle. However, the role of PAK1 and PAK2 in insulin-stimulated glucose uptake in mature 54 skeletal muscle has not been determined. The aim of the present investigation was to determine the 55 requirement for PAK1 and PAK2 in whole-body glucose homeostasis and insulin-stimulated 56 glucose uptake in skeletal muscle. Therefore, glucose uptake was measured in isolated skeletal 57 muscle incubated with a pharmacological inhibitor (IPA-3) of group I PAKs and in muscle from 58 whole-body PAK1 knockout (KO), muscle-specific PAK2 (m)KO and double whole-body PAK1 59 and muscle-specific PAK2 knockout mice. Whole-body respiratory exchange ratio, indicative of 60 substrate utilization, was largely unaffected by lack of PAK1 and/or PAK2. Whole-body glucose 61 tolerance was mildly impaired in PAK2 mKO, but not PAK1 KO mice. In contrast to a previous 62 study of GLUT4 translocation in PAK1 KO mice, PAK1 KO muscles displayed normal insulin-63 stimulated glucose uptake in vivo and in isolated muscle. On the contrary, glucose uptake was 64 slightly reduced in response to insulin in glycolytic extensor digitorum longus muscle lacking 65 PAK2. In conclusion, the current study demonstrates that group I PAKs are largely dispensable for 66 the regulation of whole-body glucose homeostasis and skeletal muscle glucose uptake. Thus, the 67 present study challenges that group I PAKs, and especially PAK1, are necessary regulators of 68 insulin-stimulated glucose uptake in skeletal muscle. 69 109Although such studies implicate group I PAKs, and in particular PAK1, in the regulation of glucose 110 homeostasis and GLUT4 translocation in skeletal muscle, the relative role of PAK1 and PAK2 in 111 insulin-stimulated glucose uptake remains to be identified in mature skeletal muscle. Therefore, we 112 performed a systematic series of pharmacologic a...