Andrews MT, Russeth KP, Drewes LR, Henry P-G. Adaptive mechanisms regulate preferred utilization of ketones in the heart and brain of a hibernating mammal during arousal from torpor. Am J Physiol Regul Integr Comp Physiol 296: R383-R393, 2009. First published December 3, 2008 doi:10.1152/ajpregu.90795.2008.-Hibernating mammals use reduced metabolism, hypothermia, and stored fat to survive up to 5 or 6 mo without feeding. We found serum levels of the fat-derived ketone, D-␤-hydroxybutyrate (BHB), are highest during deep torpor and exist in a reciprocal relationship with glucose throughout the hibernation season in the thirteen-lined ground squirrel (Spermophilus tridecemlineatus). Ketone transporter monocarboxylic acid transporter 1 (MCT1) is upregulated at the blood-brain barrier, as animals enter hibernation. Uptake and metabolism of 13 C-labeled BHB and glucose were measured by high-resolution NMR in both brain and heart at several different body temperatures ranging from 7 to 38°C. We show that BHB and glucose enter the heart and brain under conditions of depressed body temperature and heart rate but that their utilization as a fuel is highly selective. During arousal from torpor, glucose enters the brain over a wide range of body temperatures, but metabolism is minimal, as only low levels of labeled metabolites are detected. This is in contrast to BHB, which not only enters the brain but is also metabolized via the tricarboxylic acid (TCA) cycle. A similar situation is seen in the heart as both glucose and BHB are transported into the organ, but only 13 C from BHB enters the TCA cycle. This finding suggests that fuel selection is controlled at the level of individual metabolic pathways and that seasonally induced adaptive mechanisms give rise to the strategic utilization of BHB during hibernation.hibernation; ␤-hydroxybutyrate; glucose; 13 C magnetic resonance spectroscopy; blood-brain barrier NATURAL HIBERNATORS FACE UNIQUE challenges in surviving physiological extremes that would normally lead to death in most species of mammals. Profound reductions in heart rate and oxygen consumption, in conjunction with near-freezing body temperatures, require a multitude of cellular and molecular adaptations for a hibernator to avoid injury (reviewed in Ref. 1). One of the more striking adaptations is the ability to survive 5-6 mo without feeding by switching over to a lipidbased metabolism. In the absence of food, survival relies on the liberation and mobilization of fatty acids stored in the hibernator's white adipose tissue. However, some organs, most notably the brain, cannot use fat as its sole source of fuel. In this paper, we examine the hypothesis that fat-derived ketone bodies provide the critical fuel for the brain and heart during a hibernator's prolonged period of starvation.Brain function in mammals requires a relatively high rate of energy metabolism, and under normal circumstances, the predominant fuel is D-glucose. However, there are several circumstances such as starvation, diabetes, suckling neonate...

The brain of a hibernating mammal withstands physiological extremes that would result in cerebral damage and death in a non-hibernating species such as humans. To examine the possibility that this neuroprotection results from alterations in cerebral metabolism, we used in vivo 1 H NMR spectroscopy at high field (9.4 T) to measure the concentration of 18 metabolites (neurochemical profile) in the brain of 13-lined ground squirrels (Spermophilus tridecemlineatus) before, during, and after hibernation. Resolved in vivo 1 H NMR spectra were obtained even at low temperature in torpid hibernators (7°C).The phosphocreatine-to-creatine ratio was increased during torpor (+143%) indicating energy storage, and remained increased to a lesser extent during interbout arousal (IBA) (+83%). The total c-aminobutyric acid concentration was increased during torpor (+135%) and quickly returned to baseline during IBA. Glutamine (Gln) was decreased ()54%) during torpor but quickly returned to normal levels during IBA and after terminal arousal in the spring. Glutamate (Glu) was also decreased during torpor ()17%), but remained decreased during IBA ()20% compared with fall), and returned to normal level in the spring. Our observation that Glu and Gln levels are depressed in the brain of hibernators suggests that the balance between anaplerosis and loss of Glu and Gln (because of glutamatergic neurotransmission or other mechanisms) is altered in hibernation. Keywords: anaplerosis, brain, glutamate-glutamine cycle, ground squirrel, hibernation, magnetic resonance spectroscopy. The adult human brain is responsible for 20% of the body's oxygen consumption despite constituting only 2% of body weight. In contrast to the high energy demand of the human brain, torpid hibernators show a reduction in O 2 consumption by as much as 50-fold and a 10-fold reduction in cerebral blood flow, when compared with a non-hibernating animal (Frerichs et al. 1995). This considerable decrease in energy consumption is accompanied by specialized physiological adaptations including body temperature reduction approaching 0°C and a decrease in heart rate from 300 beats/min to 5-10 beats/min [reviewed in (Boyer and Barnes 1999;Frerichs 1999;Drew et al. 2001;Zhou et al. 2001;Carey et al. 2003)]. Hibernation is a regulated process involving metabolic depression (Hochachka 1986) that is controlled, in part, by the differential expression of genes common to all

A major challenge in the life sciences is the extraction of detailed molecular information from plants and animals that are not among the handful of exhaustively studied "model organisms." As a consequence, certain species with novel phenotypes are often ignored due to the lack of searchable databases, tractable genetics, stock centers, and more recently, a sequenced genome. Characterization of phenotype at the molecular level commonly relies on the identification of differentially expressed proteins by combining database searching with tandem mass spectrometry (MS) of peptides derived from protein fragmentation. However, the identification of short peptides from nonmodel organisms can be hampered by the lack of sufficient amino acid sequence homology with proteins in existing databases; therefore, a database search strategy that encompasses both identity and homology can provide stronger evidence than a single search alone. The use of multiple algorithms for database searches may also increase the probability of correct protein identification since it is unlikely that each program would produce false negative or positive hits for the same peptides. In this study, four software packages, Mascot, Pro ID, Sequest, and Pro BLAST, were compared in their ability to identify proteins from the thirteen-lined ground squirrel (Spermophilus tridecemlineatus), a hibernating mammal that lacks a completely sequenced genome. Our results show similarities as well as the degree of variability among different software packages when the identical protein database is searched. In the process of this study, we identified the up-regulation of succinyl CoA-transferase (SCOT) in the heart of hibernators. SCOT is the rate-limiting enzyme in the catabolism of ketone bodies, an important alternative fuel source during hibernation.