Biomarkers for the two phase switches of mammalian hibernation

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Mammals that hibernate depress their metabolic, heart and respiratory rates, as well as their core body temperature (Tb) to enter a state called torpor. In hibernators such as ground squirrels, torpor is precisely controlled and fully reversible using only endogenous mechanisms, yet relatively little is known about the molecular events that underlie hibernation's critical transitions. Understanding the biochemical aspects well enough to recapitulate them in a non-hibernator has profound implications for human health, offering an unprecedented opportunity to improve outcomes for victims of cardiac arrest, stroke, trauma, and hypothermia, as well as in organ transplant and routine surgery. Hibernation is an adaptive strategy for energy conservation that is exploited by many distantly related mammals; this broad phylogenetic distribution argues strongly that genetic capability underlying the phenotype is shared among mammals. Thus, we predict that an understanding of natural mammalian hibernation will lead to rational development of safe hypometabolic and protective strategies for human applications. Here we propose that hibernation comprises two biochemical switches: the first switch is a summer-to-winter switch that resets gene expression in a number of pathways leading to a protected phenotype. The second switch is a torpor-to-arousal switch that creates the heterothermic pattern characteristic to the hibernating phenotype and is responsible for reversible metabolic suppression. Markers associated with these two switches will be identified using proteomic and metabolomic techniques. The success of this work critically depends upon a carefully collected set of samples based upon the natural rhythms associated with the two switches. 21 sample groups from 13-lined ground squirrels will be analyzed, 9 for the summer-to-winter switch and 12 for the torpor-to-arousal switch. Initial focus will be on plasma, heart, lung, liver and brain, but other tissues will be collected to make a tissue bank of these valuable timepoints for additional studies and for use by the hibernation research community. Identification of these markers increases understanding of mammalian hibernation, and provides significant novel insights into natural mechanisms that achieve metabolic suppression and protection from ischemia/reperfusion injury in mammals. These markers offer an untapped source for discovery of new targets for therapeutic intervention in heart, lung and blood diseases in humans.