Project description:Hibernation is a seasonally adaptive strategy that allows hibernators to live through extreme cold condition and was viewed as a highly regulated physiological event. In spite of the profound reduction of blood flow to retina, hibernation causes no lasting retinal injury and hibernators show increased tolerance to ischemic insults during hibernation period. To understand the molecular changes of retina in response to hibernation we applied transcriptomic analysis to explore the changes of gene expression of 13-lined ground squirrel retinas during hibernation.
Project description:Mammalian hibernation is a dramatic physiological transition that involves the controlled reduction of regulated body temperature and the consequent depression of all physiological processes. The resulting reduction of metabolism and associated energy expenditure permits survival during extended periods of poor food availability in winter. To date our understanding of the molecular events that give rise to the hibernating phenotype is fragmentary and incomplete. Here, we present a large-scale gene expression screen to explore the transcriptional changes that are associated with the torpid phenotype of the hibernating golden-mantled ground squirrel, Spermophilus lateralis. Expression profiles for liver, cardiac tissue, and brain isolated from summer active, torpid, and interbout aroused animals were generated by hybridization to a squirrel microarray composed of >12,000 cDNA probes. We reveal that the transcriptional changes associated with torpor are modest and generally involve less than 2-fold changes in mRNA level. By profiling the distribution of gene ontological terms in the lists of differentially expressed genes we were able to identify the functional themes that distinguish the summer awake and hibernating phenotypes. In all tissues, the pattern of differential gene expression is consistent with a switch to lipid metabolism during hibernation. In liver, we detected an expression signature suggestive of a profound depression in urea metabolism and detoxification pathways. This expression signature was reproduced in transcript data collected from liver of the13-lined ground squirrel, S. tridecemlineatus, suggesting that this phenotype is conserved between closely related species. The transcriptional changes in cardiac tissue were interpreted as a component of the bradycardia associated with torpor. The function of the differentially expressed transcripts in brain is less transparent, likely due to heterogeneity among the responses of different cell populations in this complex organ.
Project description:Hibernating mammals undergo a dramatic drop in temperature and blood flow during torpor and must suppress hemostasis to avoid stasis blood clotting. In addition, cold storage of most mammalian platelets induces cold storage lesions, resulting in rapid clearance following transfusion. 13-lined ground squirrels (Ictidomys tridecemlineatus) provide a model to study hemostasis and cold storage of platelets during hibernation because, even with a body temperature of 4-8C, their platelets are resistant to cold storage lesions. We quantified and systematically compared proteomes of platelets collected from ground squirrels at summer (activity), fall (entrance), and winter (topor) to elucidate how molecular-level changes in platelets may support hemostatic adaptations in torpor. Platelets were isolated from squirrel blood collected in June, October, and January. Platelet lysates from each animal were digested with trypsin prior to 11-plex tandem mass tag (TMT) labeling, followed by LC-MS/MS analysis for relative protein quantification. We found over 700 platelet proteins with significant changes over the course of entrance, torpor, and activity – including systems of proteins regulating translation, platelet degranulation, metabolism, complement, and coagulation cascades. We also noted species specific differences in hemostatic, secretory, and inflammatory regulators in ground squirrel platelets relative to human platelets. In addition to providing the first ever proteomic characterization of platelets from hibernating animals, our results support a model whereby systematic changes in metabolic, hemostatic, and other proteins support physiological adaptations in torpor. In addition, our results could translate into better methods to cold store human platelets, increasing their supply and quality for transfusions.