The long-term objective of this grant has been to determine the role of glucose transport in adipose tissue and muscle in whole body glucose homeostasis and insulin sensitivity, with the goal of finding new therapeutic targets for type 2 diabetes. We demonstrated an important role for adipocytes in insulin sensitivity and the pathogenesis of type 2 diabetes. We showed that the down regulation of Glut4 in adipocytes that occurs in obesity and type 2 diabetes plays an important role in the insulin resistance in these states. We discovered that adipose expression and serum levels of retinol binding protein 4 (RBP4) are increased in insulin resistant states in humans and rodents In the next cycle, the overall goals will continue to be to determine 1) the physiologic, cellular and molecular mechanisms by which RBP4 causes insulin resistance and 2) whether increased retention of RBP4 is an important mechanism for its serum elevation in insulin resistant states, and the mechanisms underlying this.
Aim 1 is to determine the mechanisms for RBP4-induced insulin resistance. Using complementary in vivo and in vitro approaches, we will investigate the intracellular signaling pathways that appear to be involved and the "inflammatory" effects.
Aim 2 is to determine whether the mechanism(s) by which elevation of RBP4 causes insulin resistance are retinoid-dependent or retinoid-independent.
Aim 3 is to determine the role of STRA6 in RBP4-induced metabolic effects.
Aim 4 is to determine whether increased retention of RBP4 is an important mechanism for RBP4 elevation in serum in insulin-resistant states and whether this results from post-translational modifications of transthyretin. Understanding the mechanisms by which elevated RBP4 contributes to insulin resistance, metabolic syndrome and risk of diabetes and cardiovascular disease could lead to new insights into the pathogenesis of these disorders. In addition, understanding the mechanisms by which RBP4 becomes elevated in these states could lead to new therapeutic approaches. These studies will elucidate novel mechanisms underlying the inter-tissue communication that plays an important role in the pathogenesis of type 2 diabetes.
Fat cells are important regulators of metabolism and diabetes risk. Fat cells and liver secrete retinol binding protein 4 (RBP4) which carries vitamin A in the blood. RBP4 is elevated in serum of insulin resistant people with obesity and type 2 diabetes. This may contribute to the insulin resistance and risk for diabetes. We will investigate the mechanisms by which RBP4 regulates insulin/glucose balance and diabetes risk.
|Smith, U; Kahn, B B (2016) Adipose tissue regulates insulin sensitivity: role of adipogenesis, de novo lipogenesis and novel lipids. J Intern Med 280:465-475|
|Zhang, Tejia; Chen, Shili; Syed, Ismail et al. (2016) A LC-MS-based workflow for measurement of branched fatty acid esters of hydroxy fatty acids. Nat Protoc 11:747-63|
|Moraes-Vieira, Pedro M; Saghatelian, Alan; Kahn, Barbara B (2016) GLUT4 Expression in Adipocytes Regulates De Novo Lipogenesis and Levels of a Novel Class of Lipids With Antidiabetic and Anti-inflammatory Effects. Diabetes 65:1808-15|
|Moraes-Vieira, Pedro M; Castoldi, Angela; Aryal, Pratik et al. (2016) Antigen Presentation and T-Cell Activation Are Critical for RBP4-Induced Insulin Resistance. Diabetes 65:1317-27|
|Zemany, Laura; Bhanot, Sanjay; Peroni, Odile D et al. (2015) Transthyretin Antisense Oligonucleotides Lower Circulating RBP4 Levels and Improve Insulin Sensitivity in Obese Mice. Diabetes 64:1603-14|
|Kraus, Bettina J; Sartoretto, Juliano L; Polak, Pazit et al. (2015) Novel role for retinol-binding protein 4 in the regulation of blood pressure. FASEB J 29:3133-40|
|Kraus, Daniel; Yang, Qin; Kahn, Barbara B (2015) Lipid Extraction from Mouse Feces. Bio Protoc 5:|
|Moraes-Vieira, Pedro M; Yore, Mark M; Dwyer, Peter M et al. (2014) RBP4 activates antigen-presenting cells, leading to adipose tissue inflammation and systemic insulin resistance. Cell Metab 19:512-26|
|Zemany, Laura; Kraus, Bettina J; Norseen, Julie et al. (2014) Downregulation of STRA6 in adipocytes and adipose stromovascular fraction in obesity and effects of adipocyte-specific STRA6 knockdown in vivo. Mol Cell Biol 34:1170-86|
|Sun, Qi; JimÃ©nez, Monik C; Townsend, Mary K et al. (2014) Plasma levels of fetuin-A and risk of coronary heart disease in US women: the Nurses' Health Study. J Am Heart Assoc 3:e000939|
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