Glut4-mediated glucose uptake represents the rate-limiting step of insulin-stimulated glucose disposal, and type 2 diabetes is associated with impaired translocation of Glut4 to the cell surface. The insulin-responsive pool of Glut4 is localized in intracellular membrane vesicles, or IRVs, that deliver Glut4 to the plasma membrane. Proteomics analyses performed in our and other laboratories have shown that, in addition to Glut4, these vesicles contain three major proteins, sortilin, IRAP, and LRP1. Our hypothesis is that sortilin represents the proactive component of the IRVs which is responsible for their formation and insulin responsiveness, whereas other IRV proteins including Glut4 may just be passive cargo in this compartment. However, sortilin cannot perform its biological functions without regulatory proteins that interact with its cytoplasmic tail.
In Specific Aim 1, w propose to isolate and to identify these proteins by mass-spectrometry. Another important biological role of sortilin is to maintain normal levels of the Glut4 protein in adipocytes by retrieving it from endosomes. The specific mechanism of Glut4 retrieval is unknown and will be explored in Specific Aim 2. In addition to its role in the Glut4 pathway, sortilin plays an important role in protein targeting from Golgi to lysosomes. In the previous funding period, we have found that sortilin interacts with adiponectin and facilitates its lysosomal degradation thus regulating adiponectin secretion at a previously unknown post-translational level.
In Specific Aim 3, we will test the hypothesis that sortilin targets adiponectin for degradation in lysosomes in an acyl CoA-dependent fashion. In parallel, we will analyze expression levels of sortilin, adiponectin, Glut4, and several other proteins in fat samples obtained from insulin-sensitive and insulin-resistant patients undergoing bariatric surgery.

Public Health Relevance

Impaired translocation of Glut4 to the cell surface represents the key factor for the development of type 2 diabetes mellitus. Recent studies point out to the cell biology of Glut4 recycling as a potential site of primary diabetes-related abnormalities. We propose to explore several unknown aspects of Glut4 traffic which will shed light on the molecular nature of insulin resistance and diabetes.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
2R01DK052057-16A1
Application #
8882759
Study Section
Cellular Aspects of Diabetes and Obesity Study Section (CADO)
Program Officer
Haft, Carol R
Project Start
1997-02-28
Project End
2019-08-31
Budget Start
2015-09-01
Budget End
2016-08-31
Support Year
16
Fiscal Year
2015
Total Cost
Indirect Cost
Name
Boston University
Department
Biochemistry
Type
Schools of Medicine
DUNS #
604483045
City
Boston
State
MA
Country
United States
Zip Code
Zaarur, Nava; Pan, Xiang; Kandror, Konstantin V (2018) Detection of Detergent-sensitive Interactions Between Membrane Proteins. J Vis Exp :
Boesze-Battaglia, Kathleen; Walker, Lisa P; Dhingra, Anuradha et al. (2017) Internalization of the Active Subunit of the Aggregatibacter actinomycetemcomitans Cytolethal Distending Toxin Is Dependent upon Cellugyrin (Synaptogyrin 2), a Host Cell Non-Neuronal Paralog of the Synaptic Vesicle Protein, Synaptogyrin 1. Front Cell Infect Microbiol 7:469
Pan, Xiang; Zaarur, Nava; Singh, Maneet et al. (2017) Sortilin and retromer mediate retrograde transport of Glut4 in 3T3-L1 adipocytes. Mol Biol Cell 28:1667-1675
Singh, Maneet; Shin, Yu-Kyong; Yang, Xiaoqing et al. (2015) 4E-BPs Control Fat Storage by Regulating the Expression of Egr1 and ATGL. J Biol Chem 290:17331-8
Chakrabarti, Partha; Kandror, Konstantin V (2015) The role of mTOR in lipid homeostasis and diabetes progression. Curr Opin Endocrinol Diabetes Obes 22:340-6
Singh, Maneet; Kaur, Rajween; Lee, Mi-Jeong et al. (2014) Fat-specific protein 27 inhibits lipolysis by facilitating the inhibitory effect of transcription factor Egr1 on transcription of adipose triglyceride lipase. J Biol Chem 289:14481-7
Chakrabarti, Partha; Kim, Ju Youn; Singh, Maneet et al. (2013) Insulin inhibits lipolysis in adipocytes via the evolutionarily conserved mTORC1-Egr1-ATGL-mediated pathway. Mol Cell Biol 33:3659-66
Huang, Guanrong; Buckler-Pena, Dana; Nauta, Tessa et al. (2013) Insulin responsiveness of glucose transporter 4 in 3T3-L1 cells depends on the presence of sortilin. Mol Biol Cell 24:3115-22
Kim, Ju Youn; Kandror, Konstantin V (2012) The first luminal loop confers insulin responsiveness to glucose transporter 4. Mol Biol Cell 23:910-7
Karki, Shakun; Chakrabarti, Partha; Huang, Guanrong et al. (2011) The multi-level action of fatty acids on adiponectin production by fat cells. PLoS One 6:e28146

Showing the most recent 10 out of 23 publications