A basic mechanism contributing to human insulin resistance and diabetes: role of the essential amino acid sensor SLC36A4 in GLUT4 trafficking in adipocytes

About This Grant

Modified Project Summary/Abstract Section The GLUT4 transporter mediates insulin-stimulated glucose uptake into adipocytes, an essential response for whole-body glucose homeostasis. In addition to storage and release of fatty acids, adipocytes have a prominent endocrine role in the regulation of whole-body metabolism that is negatively affected by defects in adipocyte glucose uptake. Insulin promotes glucose uptake by inducing a reversible redistribution of intracellular GLUT4 to the plasma membrane (PM). We recently discovered that the amino acid (AA) transporter, PAT4 (SLC36A4) is co-concentrated with GLUT4 in a specialized region of the TGN. PAT4 was also identified in GWAS data to be associated with elevated postprandial blood glucose. In pilot studies, we have shown that PAT4 knockout in culture fat cells induces a blunting of GLUT4 translocation to the PM. The overarching objectives of this application are to mechanistically define how insulin controls PAT4, how PAT4 contributes to GLUT4 translocation, and to explore why an AA transporter is linked to GLUT4 trafficking. The central hypothesis of the project is that PAT4 has a feedforward role in insulin-stimulated GLUT4 translocation. In Aim 1, we test my hypotheses that insulin-stimulated translocation of PAT4 from the TGN to the PM is required for PAT4-dependent contribution to insulin-stimulated GLUT4 translocation. We will use genetic, cell biological, and biochemical approaches to define the molecular pathway linking insulin receptor activation to PAT4 translocation. In Aim 2, we will determine which AAs and how they are sensed by PM PAT4. These cell-based studies will address key mechanistic gaps in our understanding of nutrient input into the control of GLUT4 trafficking and they will establish PAT4 as a dynamic regulator of insulin signaling. In Aim 3, we will create an adipose-specific knockout of PAT4 using commercially available floxed PAT4 ES cells. Using these mice, we will test the metabolic consequences of adipose PAT4 deletion, including how adipocyte PAT4 deletion affects response to different diet challenges. These studies will determine if PAT4 functions as a nutrient sensor that integrates AA availability with insulin signaling to coordinate glucose uptake in adipose tissue. Overall, the proposed in vitro and in vivo studies will link cell-based mechanisms to whole-body metabolic control. Because defects in GLUT4 translocation are associated with insulin resistance and T2D, this work will advance a more complete understanding of the etiology, progression, and potentially the treatment of these conditions.