Seasonal Mitochondrial Metabolism And Adenosine Signaling In The Thirteen-Lined Ground Squirrel (Ictidomys Tridecemlineatus)

Abstract

The thirteen-lined ground squirrel (Ictidomys tridecemlineatus) undergoes extreme and rapid shifts in body temperature (Tb) during hibernation as it cycles between torpor (Tb ~ 5-10 C) and interbout arousal (IBA, Tb ~37 C). This requires regulated changes in the physiology of the tissues that produce much of the heat required during this shift, namely brown adipose tissue (BAT) and skeletal muscle. However, once normothermic body temperature is reached during arousal, production of additional heat is not needed; therefore, regulation of this whole-body heating and cooling is important. As hibernation involves coordinated responses from several organs, it is important to not only look at the function of each organ individually, but also how they influence the response of other tissues. To understand how the thirteen-lined ground squirrel regulates such extreme physiological shifts, I examined the influence of temperature and season on the function of thermogenic BAT at both the cellular and mitochondrial level by measuring respiration rates at several temperatures. Overall, I found isolated BAT mitochondria and adipocyte respiration is independent of season at each temperature measured. Since elevated adenosine has been suggested to serve as a potential means to inhibit BAT heat production by receptor-dependent processes, I also examined adenosine signaling by measuring the expression levels of proteins isolated from skeletal muscle involved in the production and transport of adenosine as well as the adenosine receptor in BAT. Two proteins involved in adenosine signaling which are differentially expressed (ADORA1 and AMPD1) could impact the function of BAT and other tissues.