Constitutively Active CaMKKα Stimulates Skeletal Muscle Glucose Uptake in Insulin-Resistant Mice In Vivo

  1. Carol A. Witczak1,2,3,4
  1. 1Department of Kinesiology, East Carolina University, Greenville, NC
  2. 2Department of Biochemistry and Molecular Biology, Brody School of Medicine, East Carolina University, Greenville, NC
  3. 3Department of Physiology, Brody School of Medicine, East Carolina University, Greenville, NC
  4. 4East Carolina Diabetes and Obesity Institute, East Carolina University, Greenville, NC
  1. Corresponding author: Carol A. Witczak, witczakc{at}ecu.edu.
  1. J.M.H. and J.L.F. contributed equally to this study.

Abstract

In insulin-sensitive skeletal muscle, the expression of constitutively active Ca2+/calmodulin-dependent protein kinase kinase α (caCaMKKα) stimulates glucose uptake independent of insulin signaling (i.e., Akt and Akt-dependent TBC1D1/TBC1D4 phosphorylation). Our objectives were to determine whether caCaMKKα 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 caCaMKKα plasmids using in vivo electroporation. After 2 weeks, caCaMKKα protein was robustly expressed. In insulin-sensitive muscle, caCaMKKα increased basal in vivo [3H]-2-deoxyglucose uptake approximately twofold, insulin increased glucose uptake approximately twofold, and caCaMKKα plus insulin increased glucose uptake approximately fourfold. caCaMKKα did not increase basal TBC1D1 (Ser237, Thr590, Ser660, pan-Thr/Ser) or TBC1D4 (Ser588, Thr642, pan-Thr/Ser) phosphorylation. In insulin-resistant muscle, caCaMKKα 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, CaMKKα increased TBC1D1 (Thr590, pan-Thr/Ser) and TBC1D4 (Ser588, pan-Thr/Ser) phosphorylation. Collectively, these results demonstrate that caCaMKKα stimulates glucose uptake additively with insulin, and in insulin-resistant muscle, and alters the phosphorylation of TBC1D1/TBC1D4.

Footnotes

  • Received March 22, 2013.
  • Accepted October 1, 2013.

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  1. Diabetes vol. 63 no. 1 142-151
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