Previous human studies have demonstrated an important role for amino acids in both protein and glucose metabolism: amino acids stimulate protein synthesis and inhibit proteolysis, but also decrease whole-body and forearm glucose disposal. Data presented in this proposal demonstrate that amino acids act as novel signaling elements in insulin target tissues both in vivo and in vitro: (1) Amino acids activate intermediates important in the initiation of protein synthesis, including p70 S6 kinase and PHAS-1, in synergy with insulin. (2) Concurrently, amino acids inhibit steps in insulin action critical for glucose transport and utilization, including tyrosine phosphorylation of insulin receptor substrates and activation of phosphatidylinositol 3-kinase (PI 3-kinase). Taken together, these data support the hypothesis that amino acids and their metabolites act as specific positive signals critical for maintenance of protein mass, yet also inhibit the action of insulin at multiple levels. This bifunctional modulation of insulin action suggests crosstalk between hormonal and nutritional signals and a novel mechanism by which nutritional factors contribute to insulin resistance. The broad goals of this proposal are to understand the cellular mechanisms by which amino acids modulate insulin signaling and to investigate the role of amino acids in the pathophysiology of insulin resistance. Our studies will be directed at four specific aims: (1) to identify the mechanisms by which amino acids stimulate p70 S6 kinase and PHAS-1 phosphorylation, (2) to identify the mechanisms by which amino acids decrease insulin-stimulated activation of PI 3-kinase and glucose transport, (3) to determine the role of amino acids in the development of insulin resistance in normal physiology, and (4) to evaluate the contribution of amino acids in rodent models of genetic insulin resistance. My training and skills in both clinical endocrinology/metabolism and basic signal transduction investigation provide me with a unique perspective to explore the exciting interface between metabolic and classical hormonal signaling systems. The continuing mentoring and support of Dr. C. Ronald Kahn, within the environment of the Joslin Diabetes Center and Longwood Medical Area, provide me with an excellent opportunity to continue my investigation and to further develop my skills to attain my goal as an independent investigator.
