The Contribution of p300/CBP and Acetylation Towards Skeletal Muscle Insulin Action

Impaired insulin-stimulated glucose uptake is a common metabolic disorder in aged and obese skeletal muscle, with this “insulin resistance” being the primary metabolic defect of type 2 diabetes. At a molecular level, skeletal muscle insulin signaling to glucose uptake is regulated by a phosphorylation-based, phosphoinositide 3-kinase (PI3K)/Akt-dependent signaling pathway. However, recent proteomic-based analysis in various tissues, including skeletal muscle, have identified more than 2000 acetylated, non-nuclear, proteins that impact a broad array of cellular processes including insulin signaling. The acetyltransferases p300 (E1A binding protein p300) and CBP (cAMP response element binding protein binding protein) are phosphorylated and activated by Akt, and p300/CBP can acetylate downstream insulin signaling and GLUT4 trafficking proteins, thus giving rise to a putative Akt-p300/CBP axis. Thus, the objective of this Dissertation was to determine the non-transcriptional importance of p300, CBP, and acetylation to skeletal muscle insulin sensitivity, for which we utilized small molecule inhibitors and muscle-specific knockout models. In Study 1, acute inhibition of deacetylases was sufficient to increase acetylation in L6 myotubes and skeletal muscle, however it did not alter insulin-stimulated glucose uptake or signaling. In Study 2, single knockout of either p300 or CBP in skeletal muscle did not impact glucose tolerance or skeletal muscle insulin action under either control, calorie restriction, or high-fat diet conditions. In Study 3, mice with combined double knockout of p300/CBP in skeletal muscle were severely glucose intolerant and skeletal muscle insulin resistant. Remarkably, this glucose intolerance and inability of skeletal muscle to respond to insulin was reversed in mice with just a single allele of either p300 or CBP. In the p300/CBP double-knockout mice, skeletal muscle insulin resistance was accompanied by significant downregulation of both mRNA and protein networks critical for insulin signaling, GLUT4 trafficking, and glucose metabolism. In summary, acutely increasing acetylation in skeletal muscle does not impact insulin stimulated glucose uptake or signaling. However, p300/CBP together are critical regulators of skeletal muscle insulin sensitivity, at least in part, by transcriptional regulation of the insulin signaling and GLUT4 trafficking pathways