Torpor in the golden-mantled ground squirrel: investigating transcriptomic dynamics across body temperature
Authors: Crippen Thomas , Barth Dylan , Carlson Zachary , van Breukelen Frank , Hindle Allyson G 
Published: May 2024

The golden-mantled ground squirrel ( Callospermophilus lateralis) is considered an elite hibernator. Seasonal torpor in the face of environmental extremes and food scarcity can elicit a decrease in body temperature to near freezing temperatures and oxygen consumption rates 1/100th of normothermic rates. Not all hibernators are capable of body temperature and metabolic depression to this degree; instead, mammalian hibernators use diverse strategies related to body size and environment and conduct torpor at body temperatures ranging from cold (rodents) to hot (bears). Tropical hibernators (tenrecs, lemurs) conduct torpor at more intermediate, warm body temperatures, and exhibit large variation in strategies. One strategy that likely enables cold-temperature torpor is control of mRNA and protein synthesis; in ground squirrels this occurs at body temperatures below 18°C. We studied the ground squirrel model as a hibernator that is capable of executing torpor over a range of temperatures, aiming to evaluate physiological and molecular strategies that vary across hot, warm, and cold torpor. We analyzed the transcriptomes of heart, brain, liver, and kidney collected from ground squirrels during the early phase of torpor bouts across a range of ambient temperatures (4, 12, 20, 25, 30°C). Temperature-responsive differential gene expression was compared between euthermic animals (37°C) and torpid animals at each experimental temperature using DESeq2. In the brain, we detected the highest number of differentially expressed genes between the non-hibernating squirrels and those torpid at 25ºC (3425 DE genes; pFDR<0.01). The highest number of differentially expressed genes for heart (2742 genes), liver (3586 genes), and kidney (2233 genes) occurred between non-hibernating animals and those torpid at 20ºC. These results suggest warm torpid temperatures around 20-25ºC induce the largest molecular response, which may indicate cellular dysregulation. Using WGCNA, we produced a consensus network of genes exhibiting correlated differential expression in all four tissues and across all pairwise comparisons between the normothermic control animals and each temperature of torpor; this network contained 488 genes. Pathway analysis within the consensus network demonstrates enrichment of key pathways related to ubiquitination, gene silencing, RNA binding, DNA repair, and alternative splicing. These pathways clearly are central to molecular responses to torpor at any temperature. Elucidating the temperature-specific differences occurring in conjunction with consensus responses will tease apart molecular strategies employed by mammals across wide-ranging hibernation phenotypes. Funded by the Translational Research Institute for Space Health. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.