Insulin resistance in skeletal muscle contributes to the metabolic derangements in obesity and Type II (non-insulin dependent) diabetes mellitus (NIDDM). Although major advances have been made in understand the mechanisms by which insulin signals its effects in muscle, much less is known regarding how abnormalities in insulin signaling contribute to insulin resistance in this tissue. We have shown that although insulin stimulated insulin receptor tyrosine phosphorylation is considerably reduced in muscle biopsies from patients with NIDDM, with consequent decreased in IRS-1 and PI 3-kinases signaling, insulin normally activates the MAP kinases cascade in these very insulin resistant patients. The overall goal of this proposal is to further characterize insulin resistance with respect to the PI 3-kinase pathway in obese and NIDDM patients and to begin to discern the mechanisms responsible for the discordance in insulin resistance with respect to the PI 3-kinase pathway in obese and NIDDM patients and to begin to discern the mechanisms responsible for the discordance insulin signaling to the PI 3-kinase and MAP kinase pathways. Specifically, we propose 1) To determine the nature of the abnormalities in insulin signaling in muscle from patients with Type II diabetes. We will test the hypothesis a) that the maximal response is reduced and the time course is altered, and we will continue to explore the mechanisms underlying our observation that insulin resistance is restricted to PI 3-kinase and does not affect the MAP kinase pathway, 2) that IRS-2 signaling is regulated differently than IRS-1 in muscle of diabetics, and 3) that the IGF-I receptor or IGF-1/insulin hybrid receptor are activated by insulin, and could potentially contribute to signaling to the MAP kinase pathway. We also propose 2) to more closely examine the mechanisms involved in the decrease in insulin stimulation or insulin receptor tyrosine phosphorylation in muscle from Type II diabetics. We will test the hypothesis that a) insulin receptor tyrosine kinase (IRTK) activity is not as reduced as insulin receptor autophosphorylation, especially toward exogenous substrates, b) increased serine phosphorylation of the receptor inhibits tyrosine phosphorylation in diabetics, and 3) that the inhibitory protein Grb-IR association with the insulin receptor is greater in diabetics than in control.
Showing the most recent 10 out of 66 publications
