Ca2+/calmodulin-dependent protein kinase kinase-α regulates skeletal muscle glucose uptake independent of AMP-activated protein kinase and Akt activation

Studies in nonmuscle cells have demonstrated that Ca2+/ calmodulin-dependent protein kinase kinases (CaMKKs) are upstream regulators of AMP-activated protein kinase (AMPK) and Akt. In skeletal muscle, activation of AMPK and Akt has been implicated in the regulation of glucose uptake. The objective of this study was to determine whether CaMKK alpha regulates skeletal muscle glucose uptake, and whether it is dependent on AMPK and/or Akt activation. Expression vectors containing constitutively active CaMKK alpha (caCaMKK alpha) or empty vector were transfected into mouse muscles by in vivo electroporation. After 2 weeks, caCaMKK alpha was robustly expressed and increased CaMKI (Thr(177/180)) phosphorylation, a known CaMKK substrate. In muscles from wild-type mice, caCaMKKa increased in vivo [H-3]-2-deoxyglucose uptake 2.5-fold and AMPK alpha 1 and -alpha 2 activities 2.5-fold. However, in muscles from AMPK alpha 2 inactive mice (AMPK alpha 2i), caCaMKK alpha did not increase AMPK alpha 1 or -a2 activities, but it did increase glucose uptake 2.5-fold, demonstrating that caCaMKKa stimulates glucose uptake independent of AMPK. Akt (Thr(308)) phosphorylation was not altered by CaMKK alpha, and caCaMKKa plus insulin stimulation did not increase the insulin-induced phosphorylation of Akt (Thr(308)). These results suggest that caCaMKKa stimulates glucose uptake via insulin-independent signaling mechanisms. To assess the role of CaMKK in contraction-stimulated glucose uptake, isolated muscles were treated with or without the CaMKK inhibitor STO-609 and then electrically stimulated to contract. Contraction increased glucose uptake 3.5-fold in muscles from both wild-type and AMPKa2i mice, but STO-609 significantly decreased glucose uptake (similar to 24%) only in AMPKa2i mice. Collectively, these results implicate CaMKK alpha in the regulation of skeletal muscle glucose uptake independent of AMPK and Akt activation.