All ETDs from UAB

Advisory Committee Chair

W Timothy Garvey

Advisory Committee Members

Aimee Landar

Yabing Chen

Yuchang Fu

Tim M Townes

W Timothy Garvey

Document Type

Dissertation

Date of Award

2013

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Insulin resistance plays a central role in the pathogenesis of Type 2 Diabetes (T2DM) and involves diminished stimulation of glucose transport in skeletal muscle. Improvements in insulin sensitivity are essential for both prevention and treatment of T2DM. However, the limitation of current medications highlights the need for alternative molecular regulators of insulin action and developing new insulin sensitizers. Our laboratory has initially identified roles for the orphan nuclear receptor NR4A3 in insulin-sensitization and stimulation of glucose transport. However, the cellular effect and downstream mechanisms of NR4A3 and its agonists (e.g. 6-mercaptopurine/6-MP) on insulin effector system in skeletal muscle remain unknown. Moreover, since no ligands have been discovered for NR4A3, it is necessary to identify novel ligands or co-transactivators for NR4A3 that are effective in glucose metabolism and insulin action. Our goal is to improve understanding of the roles of NR4A3 and its agonists in regulating insulin action, and its rationale as a therapeutic drug target for treating insulin resistance. To achieve this goal, in the first portion of this dissertation, I examined the effects and mechanisms of NR4A3 and a potential NR4A3 agonist 6-MP on glucose transport and insulin action in L6 skeletal muscle cells. I have demonstrated that 6-MP augments glucose transport activity via increasing GLUT4 translocation in an NR4A3-dependent manner, even in the absence of insulin. I have also found 6-MP increases AS160 phosphorylation independent of NR4A3. In the second portion, I established a mammalian cell-based "one-hybrid" luciferase assay system for high-throughput screening of potential NR4A3 activating ligands. From screening 130K compounds in combinatorial libraries, I have identified 430 hits that meet criteria for high activity. I further characterized three of these novel NR4A3 agonists for their roles in muscle glucose transport and insulin sensitivity in vitro and in vivo. These agonists augment glucose transport and GLUT4 translocation in L6 muscle cells in an NR4A3-dependent manner, and administration to female db/db mice improves systemic glucose tolerance and insulin sensitivity. Overall, these findings provide proof-of-principle for NR4A3 as a novel therapeutic target, and for development of agonists to treat insulin resistance in patients with T2DM and other metabolic disorders.

Share

COinS