Constitutively Active CaMKKa Stimulates Skeletal Muscle

In insulin-sensitive skeletal muscle, the expression of constitutively active Ca2+/calmodulin-dependent protein kinase kinase a (caCaMKKa) stimulates glucose uptake independent of insulin signaling (i.e., Akt and Akt-dependent TBC1D1/TBC1D4 phosphorylation). Our objectives were to determine whether caCaMKKa could stimulate glucose uptake additively with insulin in insulin-sensitive muscle, in the basal state in insulin-resistant muscle, and if so, to determine whether the effects were associated with altered TBC1D1/TBC1D4 phosphorylation. Mice were fed a control or high-fat diet (60 % kcal) for 12 weeks to induce insulin resistance. Muscles were transfected with empty vector or caCaMKKa plasmids using in vivo electroporation. After 2 weeks, caCaMKKa protein was robustly expressed. In insulin-sensitive muscle, caCaMKKa increased basal in vivo [3H]-2-deoxyglucose uptake approximately twofold, insulin increased glucose uptake approximately twofold, and caCaMKKa plus insulin increased glucose uptake approximately fourfold. caCaMKKa did not increase basal TBC1D1 (Ser237, Thr590, Ser660, pan-Thr/Ser) or TBC1D4 (Ser588, Thr642, pan-Thr/Ser) phosphorylation. In insulin-resistant muscle, caCaMKKa increased basal glucose uptake approximately twofold, and attenuated high-fat diet–induced basal TBC1D1 (Thr590, pan-Thr/Ser) and TBC1D4 (Ser588, Thr642, pan-Thr/Ser) phosphorylation. In cell-free assays