Skeletal Muscle Glucose Transport: Exercise and Insulin

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DESCRIPTION (provided by applicant): Insulin resistance for glucose disposal by skeletal muscle is an essential and perhaps primary defect for Type 2 diabetes. The broad, long-term objective is to fully understand the mechanisms whereby insulin-and exercise intersect to co-regulate skeletal muscle glucose transport, a rate-limiting step for glucose disposal. In this project, we focus on a key health benefit of acute exercise: a substantial and long-lasting increase in insulin-stimulated glucose transport. We will test a novel model that proposes that the mechanism for this exercise effect begins with, Triggering Events (essential and transient prerequisites) that induce 1 or more Memory Element (persistent, post-exercise outcomes linking triggers to downstream mediators). After exercise, Mediators are the key insulin signaling steps that, as a consequence of Memory Elements, and upon engagement by a physiologic insulin concentration, lead to improved insulin action. The Mediators lead to increased cell-surface localized GLUT4, which is the End-effector ultimately responsible for increased insulin-stimulated glucose transport. We have 4 Specific Aims: 1) Determine if elements of the humoral kallikrein-kinin system (KKS) are essential triggers for elevated post-exercise glucose transport in insulin- stimulated skeletal muscle. 2) Determine if AMP-activated protein kinase (AMPK) is an essential trigger for post-exercise elevation in insulin-stimulated glucose transport in skeletal muscle. 3) Elucidate the effects of insulin and exercise on the amount of GLUT4 associated with TUG (TUG-GLUT4) and determine the relationship of putative triggers (humoral-KKS and AMPK) with TUG-GLUT4. 4) Identify sequential links from triggers to memory elements to insulin signaling; steps that mediate GLUT4 recruitment to the cell surface thereby leading to elevated insulin-stimulated glucose transport. We will probe relationships among the model's components because only a comprehensive approach can reveal the integrated mechanisms for this complex process. Because physical activity is all too common, millions of Americans can potentially improve their insulin sensitivity via exercise. Illuminating the mechanisms for post-exercise improvement in insulin action should facilitate the design of optimal exercise programs for each person's abilities and development of other interventions to improve insulin action in those who cannot perform sufficient exercise.