The Squirrel Heart, Temperature, and Hibernation

Some mammals have evolved to hibernate during periods of low resource availability, such as during colder seasons in temperate climates. During hibernation, animals cycle through states of torpor and short periods of arousal. When going into torpor, these mammals will drop their body temperature to around 4oC to conserve energy normally used to keep warm. This leads to a reduction in enzymatic activity and metabolic rates. To investigate the importance of hibernating at 4oC compared to warmer temperatures (12oC, 20oC, 25oC, 30oC) and how normally active tissues function at these temperatures, heart samples were collected from hibernating golden-mantled ground squirrels (Callospermophilus lateralis). We isolated proteins from the samples and prepared them for LC-MS/MS, which involved protein denaturation, reduction, alkylation, digestion, peptide desalting, and peptide quantification. Mass spectra produced by LC-MS/MS were used to identify proteins, quantify their abundances, and then compare them between Tb groups. In total, we identified 1228 proteins in the ground squirrel heart proteome. Examples of proteins that differed in abundance between temperature groups included succinate dehydrogenase assembly factor 2, which was higher at colder temperatures and hemoglobin subunit beta, which was higher at warmer temperatures. This information can be applied in future studies about hibernation, especially in the context of temperature fluctuations caused by global warming. Looking at the differences in proteins present during hibernation in lower versus higher temperatures will allow for future predictions on how mammals' abilities to hibernate will be affected. Hibernation is an important process performed by mammals since it allows for survival during harsh conditions, which in turn helps increase their lifespan. In future studies, differences in protein expression can anticipate the fitness of hibernators affected by climate change.