Insulin And Non-Insulin Dependent Glut4 Trafficking Regulation By The Tug Protein

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Yale Medicine Thesis Digital Library School of Medicine

January 2019

Insulin And Non-Insulin Dependent Glut4

Trafficking: Regulation By The Tug Protein

Stephen Devries

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Recommended Citation

Devries, Stephen, "Insulin And Non-Insulin Dependent Glut4 Trafficking: Regulation By The Tug Protein" (2019). Yale Medicine

Thesis Digital Library. 3489.

https://elischolar.library.yale.edu/ymtdl/3489

Insulin and non-insulin dependent GLUT4 trafficking:

regulation by the TUG protein

A Thesis Submitted to

the Yale University School of Medicine

in Partial Fulfillment of the Requirements for the

Degree of Doctor of Medicine

by

Stephen Graham DeVries

2019

Abstract

The body tightly regulates glucose production and disposal despite changing

metabolic demands, including large post-prandial and fasting fluctuations. Specifically,

under the action of insulin, muscle contraction, ischemia, and poor nutrient availability,

cells increase the amount of the glucose transporter type 4 (GLUT4) at the plasma

membrane by mobilizing a sequestered pool of transporters. In this work, we demonstrate

that the TUG (tether containing a UBX domain for GLUT4) protein mediates both

insulin-dependent and insulin-independent pathways to increase GLUT4 at the plasma

membrane. In mice fed a high fat diet to induce insulin resistance, the regulation of the

endoproteolytic cleavage of the TUG protein was disrupted. We also present evidence

that helps to identify the key protease, Usp25m, that cleaves the tethering protein TUG in

both an insulin-dependent and insulin-independent manner, releasing GLUT4 from its

storage location in the basal state to the plasma membrane in an activated state. Finally,

our results also suggest that in the adipocytes and myocytes, activated AMPK leads to

cleavage of the TUG protein.

Acknowledgements

I would like to thank Dr. Estifanos Habtemichael, who patiently taught me the

techniques necessary to work in a cell biology laboratory at the beginning of medical

school. His constant guidance and feedback were invaluable to the work that led to this

thesis. I would also like to thank Don Li, who helped me adapt and optimize my planned

projects. His mentoring both in research and in medical training has been a central part of

my training as a physician and as a scientist. Finally, I would like to thank my advisor,

Dr. Jonathan Bogan, whose constant enthusiasm for science, optimism, and support made

working in his lab the highlight of my time in medical school.

Table of contents

1. Introduction 1

1.1. Insulin resistance 1

1.2. Macronutrient contributions to obesity 5

1.3. GLUT4 transporters and their regulation by membrane trafficking 7

1.4. Thyroid hormone agonists 15

1.5. Exercise-induced glucose uptake in muscle and the role of AMPK 16

1.6. Mouse model of type 2 diabetes mellitus 21

2. Statement of purpose, specific hypothesis, and specific aims 22

3. Methods 23

3.1. Reagents and cell culture 23

3.2. Mice 25

4. Results 26

4.1. Usp25m interacts with TUG 26

4.2. TUG cleavage differences in HFD and RC fed mice 27

4.3. Activated AMPK 27

5. Discussion 35

5.1. Usp25m interacts with TUG 35

5.2. HFD inhibits TUG cleavage 36

5.3. AMPK 36

References 39