As the epidemic of insulin resistance and type 2 diabetes emerges worldwide, there is an urgent need to understand how insulin maintains blood glucose homeostasis at the molecular level. A major function of insulin is to promote glucose uptake into muscle and adipose tissues, a process mediated by the glucose transporter GLUT4. Upon insulin stimulation, GLUT4 is relocated from intracellular storage vesicles to the cell surface through regulated exocytosis. The exocytosis of GLUT4 vesicles requires the SNARE proteins as the core fusion machinery, as well as a group of fusion regulators. Loss-of-function mutations of the SNAREs or fusion regulators 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 understood how they act in concert to mediate and regulate GLUT4 vesicle fusion. The overall goal of this proposal is to answer this key question using novel and complementary approaches. We will first define the molecular mechanisms and functional interactions of the vesicle fusion proteins using a novel reconstituted fusion system. We will use both recombinant proteins and native proteins isolated from mouse adipocytes. We will then characterize GLUT4 vesicle fusion proteins in 3T3-L1 adipocytes and in adipocytes isolated from knockout mice. Finally, we will determine whether and how the activities of the vesicle fusion proteins are impaired in insulin resistance, using hig 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 insulin resistance and type 2 diabetes, and will facilitate the development of novel strategies for therapeutic intervention.

Public Health Relevance

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.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
1R01DK095367-01A1
Application #
8437981
Study Section
Cellular Aspects of Diabetes and Obesity Study Section (CADO)
Program Officer
Haft, Carol R
Project Start
2013-04-01
Project End
2018-03-31
Budget Start
2013-04-01
Budget End
2014-03-31
Support Year
1
Fiscal Year
2013
Total Cost
$331,688
Indirect Cost
$114,188
Name
University of Colorado at Boulder
Department
Biochemistry
Type
Schools of Arts and Sciences
DUNS #
007431505
City
Boulder
State
CO
Country
United States
Zip Code
80309