Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Biology

Supervisor

Staples, James F.

Abstract

Some species of hibernating endotherms suppress whole body metabolism by approximately 95%. I hypothesized that post-translational modifications (PTMs) of mitochondrial proteins regulate the reversible suppression of mitochondrial metabolism during hibernation. I predicted that abundance of PTMs between torpor and euthermic states of hibernation would differ based on the regulatory action of the modification. I compared abundance of acetylation, hydroxylation, phosphorylation, succinylation, sulfhydration, SUMOylation, and S-nitrosylation in torpid, interbout euthermic, and summer euthermic thirteen-lined ground squirrels (TLGS) using one-dimensional immunoblotting. I then used two-dimensional immunoblotting for PTMs displaying many significant differences among groups to further characterize differentially modified proteins. I observed differential modifications in proteins of various molecular masses among experimental groups in all one and two-dimensional immunoblots. My findings demonstrate that PTMs of mitochondrial proteins differ among physiological states, correlating with changes in liver mitochondrial respiration, supporting that reversible suppression of mitochondrial respiration during hibernation may be regulated by PTMs.

Summary for Lay Audience

When small mammals experience cold conditions in the winter, it is metabolically costly for them to maintain their normal body temperature. One strategy for avoiding this metabolically expensive challenge is to hibernate. During hibernation, body temperature as well as many other physiological processes are significantly lowered; metabolism specifically is lowered to less than 10% of an animal’s normal rate. This lowering of metabolism will last for the whole winter in a cyclical pattern. Metabolism is lowered for about two weeks and is then interrupted by an 8–12-hour phase during which it temporarily returns to normal. After this, the animal will return to having a low metabolic rate once again and will repeat this cycle until early spring.

Our species of interest, the thirteen-lined ground squirrel (TLGS), hibernates over the winter in an obligate manner, meaning they will hibernate and suppress their metabolism regardless of any external cues. The mechanism that causes a TLGS to hibernate and lower their metabolism is not well understood. We know that mitochondria are the powerhouses of cells and are responsible for a considerable amount of energy production, so I decided to investigate reversible, post-translational modifications (meaning modifications made after a protein is first synthesized by a cell) on proteins in mitochondria as a potential way that squirrels regulate metabolic suppression during hibernation.

I studied seven different types of post-translational modifications of proteins in the mitochondria among torpor, IBE, and summer squirrels to identify if there were any differences among groups. Across all seven post-translational modifications I assessed there were significant differences among torpor, IBE, and summer squirrels. This result supported my prediction that post-translational modification of mitochondrial proteins may be how TLGS are regulating metabolic suppression in hibernation.

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