As the epidemic of insulin resistance and type 2 diabetes emerges worldwide, there is an urgent need tounderstand how insulin maintains blood glucose homeostasis at the molecular level. A major function of insulinis to promote glucose uptake into muscle and adipose tissues, a process mediated by the glucose transporterGLUT4. Upon insulin stimulation, GLUT4 is relocated from intracellular storage vesicles to the cell surfacethrough regulated exocytosis. The exocytosis of GLUT4 vesicles requires the SNARE proteins as the corefusion machinery, as well as a group of fusion regulators. Loss-of-function mutations of the SNAREs or fusionregulators abrogate insulin-triggered GLUT4 exocytosis and disrupt blood glucose homeostasis. Moreover,imbalances in the GLUT4 vesicle fusion proteins have been implicated in obesity-associated insulin resistance.While the physiological importance of the SNAREs and fusion regulators is clear, it remains poorly understoodhow they act in concert to mediate and regulate GLUT4 vesicle fusion. The overall goal of this proposal is toanswer this key question using novel and complementary approaches. We will first define the molecularmechanisms and functional interactions of the vesicle fusion proteins using a novel reconstituted fusionsystem. We will use both recombinant proteins and native proteins isolated from mouse adipocytes. We willthen characterize GLUT4 vesicle fusion proteins in 3T3-L1 adipocytes and in adipocytes isolated fromknockout mice. Finally, we will determine whether and how the activities of the vesicle fusion proteins areimpaired in insulin resistance, using high fat diet-fed mice as a model system. If successfully accomplished,this research will substantially broaden our knowledge about the regulatory mechanisms of GLUT4 exocytosis.The findings will also shed light upon the diseases associated with glucose imbalances such as insulinresistance and type 2 diabetes, and will facilitate the development of novel strategies for therapeuticintervention.
Insulin-triggered exocytosis of the glucose transporter GLUT4 plays a key role in maintaining blood glucose homeostasis. Imbalances in the GLUT4 pathway can give rise to insulin resistance and type 2 diabetes. Knowledge of the protein-protein networks that mediate and regulate GLUT4 exocytosis will shed light upon the pathogenesis of type 2 diabetes and will likely identify novel targets for therapeutic intervention.
