Alterations in Post-Receptor Insulin Signaling in Diabetes and Insulin Resistance

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Abstract: This is a revised grant application entitled “Alterations in Post-Receptor Insulin Signaling in Diabetes and Insulin Resistance.” Insulin and IGF-1 acting via their cognate receptors (IR and IGF1R) to produce a wide range of metabolic and growth effects on most cells in the body. Over many years, work from my lab has been devoted to understanding the intermediate signals in this process and how these may be altered in disease. Thus, we have characterized extensively the roles of insulin receptor substrate proteins in coupling IR and IGF1R to downstream effector systems, the important role of PI-3 kinase and Akt in the metabolic actions of insulin, and effects of MAP/mTOR/S6K kinase pathway in growth promotion. These studies have led to development of an integrated model of the insulin signaling network in which there are critical nodes of signal divergence that provide complementary information to different downstream actions of insulin. These critical nodes also provide important sites of positive and negative regulation that can lead to alterations of insulin action in disease. Recently, we have begun to dissect the full phosphoproteome downstream IR/IGF1R and, through this, have identified two new Forkhead transcriptional mediators of insulin/IGF-1 signaling, FoxK1 and FoxK2. From a disease perspective, we have also shown how different insulin resistant states alter the insulin signaling network in different tissues. We have also developed iPS cell models to focus on identification of cell autonomous components of insulin resistance in human disease. Indeed, as shown in our preliminary data, myoblasts derived from T2D iPSCs demonstrate defects in downstream signaling and metabolic function in vitro mirroring the defects found in vivo. More importantly, these cells also show dysregulation of a multidimensional phosphorylation network - both inside and outside the classical insulin signaling cascade. In this grant, we will focus on two interrelated specific aims: 1) Elucidate the fundamental differences in insulin signaling in T2D and other insulin resistant states in vitro using targeted and global phosphoproteomics of human iPS cell-derived myoblasts from normal individuals, T2D patients and non-diabetic individuals with insulin resistance. We will assess how these changes affect cellular function and participate in insulin resistance. 2) Define the role of two new downstream transcriptional regulators in insulin action, FoxK1 and FoxK2. We will identify the genes regulated by FoxK1/2, determine how they complement other transcriptional regulators in insulin regulation of cellular function, and how they are altered in diabetes. We will also define FoxK regulated genes using Chip-Seq. Finally, we will create mice with tissue specific deletion of FoxK1, FoxK2 and selected combinatorial knockouts to define their complementary roles in insulin-regulated gene expression and insulin action in vivo. Together these studies will lead to a new level of understanding insulin signaling and its alterations in diabetes, provide deeper understanding of insulin regulation of gene expression and provide new points for therapy of type 2 diabetes and other insulin resistant disorders.