Abstract
Mammals that enter deep hibernation experience extreme reductions in body temperature and in metabolic, respiratory, and heart rates for several weeks at a time. Survival of these extremes likely entails a highly regulated network of tissue- and time-specific gene expression patterns that remain largely unknown. To date, studies to identify differentially-expressed genes have employed a candidate gene approach or in a few cases broader unbiased screens at the RNA level. Here we use a proteomic approach to compare and identify differentially expressed liver proteins from two seasonal stages in the golden-mantled ground squirrel (summer and entrance into torpor) using two-dimensional gels followed by MS/MS. Eighty-four two-dimensional gel spots were found that quantitatively alter with the hibernation season, 68 of which gave unambiguous identifications based on similarity to sequences in the available mammalian database. Based on what is known of these proteins from prior research, they are involved in a variety of cellular processes including protein turnover, detoxification, purine biosynthesis, gluconeogenesis, lipid metabolism and mobility, ketone body formation, cell structure, and redox balance. A number of the enzymes found to change seasonally are known to be either rate-limiting or first enzymes in a metabolic pathway, indicating key roles in metabolic control. Functional roles are proposed to explain the changes seen in protein levels and their potential influence on the phenotype of hibernation.
Highlights
Mammals that enter deep hibernation experience extreme reductions in body temperature and in metabolic, respiratory, and heart rates for several weeks at a time
Homeostasis is maintained by means of the fine-tuning of cellular processes that find their basis in differential patterns of gene expression and protein activity
Gene expression in the summer active liver is expected to resemble that of any euthermic mammalian liver; whereas during the hibernation season this expression pattern could change to reflect the unique biochemistry of hibernation
Summary
2D, two-dimensional; SA, summer active; Ent, entrance; ET, early torpor; LT, late torpor; Ar, Arousing; IBA, interbout aroused; ID, identification; FABP, fatty acid-binding protein; FTHFD, 10 formyltetrahydrofolate dehydrogenase; 10 formyl THF, 10 formyltetrahydrofolate; PEPCK, phosphoenolpyruvate carboxykinase 2; PEP, phosphoenolpyruvate. The cellular machinery required for protein protection, stability, and turnover and for redox balance in the cell is expected to undergo changes with respect to season [3] These are a few of the many processes that could be affected at the protein level in the hibernator. Earlier we proposed that interbout arousals might be essential to restore gene products that are slowly lost during torpor [23] If this is the case, animals re-entering torpor after a replenishing period of interbout arousal will have fully restored their complement of required proteins; protein samples from nine SA animals were compared with the same from nine entrance (Ent) animals. The results from this study significantly enhance our current comprehensive understanding of the biochemical basis of the hibernating phenotype
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