Comparative study of HP-27 gene promoter activities between the chipmunk and tree squirrel

Differential AMPK-mediated metabolic regulation observed in hibernation-style polymorphisms in Siberian chipmunks

Hibernation is a unique physiological phenomenon allowing extreme hypothermia in endothermic mammals. Hypometabolism and hypothermia tolerance in hibernating animals have been investigated with particular interest; recently, studies of cultured cells and manipulation of the nervous system have made it possible to reproduce physiological states related to hypothermia induction. However, much remains unknown about the periodic regulation of hibernation. In particular, the physiological mechanisms facilitating the switch from an active state to a hibernation period, including behavioral changes and the acquisition of hypothermia tolerance remain to be elucidated. AMPK is a protein known to play a central role not only in feeding behavior but also in metabolic regulation in response to starvation. Our previous research has revealed that chipmunks activate AMPK in the brain during hibernation. However, whether AMPK is activated during winter in non-hibernating animals is unknown. Previous comparative studies between hibernating and non-hibernating animals have often been conducted between different species, consequently it has been impossible to account for the effects of phylogenetic differences. Our long-term monitoring of siberian chipmunks, has revealed intraspecific variation between those individuals that hibernate annually and those that never become hypothermic. Apparent differences were found between hibernating and non-hibernating types with seasonal changes in lifespan and blood HP levels. By comparing seasonal changes in AMPK activity between these polymorphisms, we clarified the relationship between hibernation and AMPK regulation. In hibernating types, phosphorylation of p-AMPK and p-ACC was enhanced throughout the brain during hibernation, indicating that AMPK-mediated metabolic regulation is activated. In non-hibernating types, AMPK and ACC were not seasonally activated. In addition, AMPK activation in the hypothalamus had already begun during high Tb before hibernation. Changes in AMPK activity in the brain during hibernation may be driven by circannual rhythms, suggesting a hibernation-regulatory mechanism involving AMPK activation independent of Tb. The differences in brain AMPK regulation between hibernators and non-hibernators revealed in this study were based on a single species thus did not involve phylogenetic differences, thereby supporting the importance of brain temperature-independent AMPK activation in regulating seasonal metabolism in hibernating animals.

Advances and applications of environmental stress adaptation research

Evolution has produced animals that survive extreme fluctuations in environmental conditions including freezing temperatures, anoxia, desiccating conditions, and prolonged periods without food. For example, the wood frog survives whole-body freezing every winter, arresting all gross physiological functions, but recovers functions upon thawing in the spring. Likewise, many small mammals hibernate for months at a time with minimal metabolic activity, organ perfusion, and movement, yet do not suffer significant muscle atrophy upon arousal. These conditions and the biochemical adaptations employed to deal with them can be viewed as Nature's answer to problems that humans wish to answer, particularly in a biomedical context. This review focuses on recent advances in the field of animal environmental stress adaptation, starting with an emphasis on new areas of research such as epigenetics and microRNA. We then examine new and emerging technologies such as genome editing, novel sequencing applications, and single cell analysis and how these can push us closer to a deeper understanding of biochemical adaptation. Next, evaluate the potential contributions of new high-throughput technologies (e.g. next-generation sequencing, mass spectrometry proteomics) to better understanding the adaptations that support these extreme phenotypes. Concluding, we examine some of the human applications that can be gained from understanding the principles of biochemical adaptation including organ preservation and treatments for conditions such as ischemic stroke and muscle disuse atrophy.

Growth promotion in pigs by oxytetracycline coincides with down regulation of serum inflammatory parameters and of hibernation-associated protein HP-27

The growth promoting effect of supplementing animal feed with antibiotics like tetracycline has traditionally been attributed to their antibiotic character. However, more evidence has been accumulated on their direct anti-inflammatory effect during the last two decades. Here we used a pig model to explore the systemic molecular effect of feed supplementation with sub therapeutic levels of oxytetracycline (OTC) by analysis of serum proteome changes. Results showed that OTC promoted growth, coinciding with a significant down regulation of different serum proteins related to inflammation, oxidation and lipid metabolism, confirming the anti-inflammatory mechanism of OTC. Interestingly, apart from the classic acute phase reactants also down regulation was seen of a hibernation associated plasma protein (HP-27), which is to our knowledge the first description in pigs. Although the exact function in non-hibernators is unclear, down regulation of HP-27 could be consistent with increased appetite, which is possibly linked to the anti-inflammatory action of OTC. Given that pigs are good models for human medicine due to their genetic and physiologic resemblance, the present results might also be used for rational intervention in human diseases in which inflammation plays an important role such as obesity, type 2 diabetes and cardiovascular diseases.

Seasonal oscillation of liver-derived hibernation protein complex in the central nervous system of non-hibernating mammals

Mammalian hibernation elicits profound changes in whole-body physiology. The liver-derived hibernation protein (HP) complex, consisting of HP-20, HP-25 and HP-27, was shown to oscillate circannually, and this oscillation in the central nervous system (CNS) was suggested to play a role in hibernation. The HP complex has been found in hibernating chipmunks but not in related non-hibernating tree squirrels, leading to the suggestion that hibernation-specific genes may underlie the origin of hibernation. Here, we show that non-hibernating mammals express and regulate the conserved homologous HP complex in a seasonal manner, independent of hibernation. Comparative analyses of cow and chipmunk HPs revealed extensive biochemical and structural conservations. These include liver-specific expression, assembly of distinct heteromeric complexes that circulate in the blood and cerebrospinal fluid, and the striking seasonal oscillation of the HP levels in the blood and CNS. Central administration of recombinant HPs affected food intake in mice, without altering body temperature, physical activity levels or energy expenditure. Our results demonstrate that HP complex is not unique to the hibernators and suggest that the HP-regulated liver-brain circuit may couple seasonal changes in the environment to alterations in physiology.

Mass spectrometric analysis of activity-dependent changes of neuropeptide profile in the snail, Helix pomatia

Terrestrial snails are able to transform themselves into inactivity ceasing their behavioral activity under unfavorable environmental conditions. In the present study, we report on the activity-dependent changes of the peptide and/or polypeptide profile in the brain and hemolymph of the snail, Helix pomatia, using MALDI TOF and quadrupole mass spectrometry. The present data indicate that the snails respond to low temperature by increasing or decreasing the output of selected peptides. Average mass spectra of the brain and hemolymph revealed numerous peaks predominantly present during the active state (19 and 10 peptides/polypeptides, respectively), while others were observed only during hibernation (11 and 13). However, there were peptides and/or polypeptides or their fragments present irrespective of the activity states (49 and 18). The intensity of fourteen peaks that correspond to previously identified neuropeptides varied in the brain of active snails compared to those of hibernating animals. Among those the intensity of eight peptides increased significantly in active animals while in hibernated animals the intensity of another six peptides increased significantly. A new peptide or peptide fragment at m/z 1110.7 was identified in a brain of the snail with the following suggested amino acid sequence: GSGASGSMPATTS. This peptide was found to be more abundant in active animals because the intensity of the peptide was significantly higher compared to hibernating animals. In summary, our results revealed substantial differences in the peptide/polypeptide profile of the brain and hemolymph of active and hibernating snails suggesting a possible contribution of peptides in the process of hibernation.

Advances in molecular biology of hibernation in mammals

Mammalian hibernation is characterized by profound reductions in metabolism, oxygen consumption and heart rate. As a result, the animal enters a state of suspended animation where core body temperatures can plummet as low as -2.9 degrees C. Not only can hibernating mammals survive these physiological extremes, but they also return to a normothermic state of activity without reperfusion injury or other ill effects. This review examines recent findings on the genes, proteins and small molecules that control the induction and maintenance of hibernation in mammals. The molecular events involved with remodeling metabolism, inducing hypothermia and maintaining organ function are discussed and considered with respect to analogous processes in non-hibernating mammals such as mice and humans. The advent of sequenced genomes from three distantly related hibernators, a bat, hedgehog and ground squirrel, provides additional opportunities for molecular biologists to explore the mechanistic aspects of this biological adaptation in greater detail.

CpG methylation at the USF-binding site is important for the liver-specific transcription of the chipmunk HP-27 gene

The chipmunk hibernation-specific HP-27 gene is expressed specifically in the liver and has a CpG-poor promoter. To reveal how the liver-specific transcription of the HP-27 gene is regulated, we performed yeast one-hybrid screening of a chipmunk liver cDNA library. A 5'-flanking sequence of the HP-27 gene, extending from -170 to -140 and containing an E-box (5'-CACGTG-3'), is essential for the liver-specific transcription of HP-27. We used this sequence as bait and found that a ubiquitously expressed transcription factor, USF (upstream stimulatory factor), bound to the E-box. In COS-7 cells, USF activated transcription from the HP-27 gene promoter. We then used bisulphite genomic sequencing to analyse the methylation status of the four CpG dinucleotides that lie in the 5'-flanking sequence of the HP-27 gene up to -450, to investigate how the ubiquitously expressed USF activates transcription of the HP-27 gene only in the liver, while its transcription is repressed elsewhere. The only difference in methylation in the tissues tested was in the CpG dinucleotide in the USF-binding site, which was hypomethylated in the liver, but highly methylated in the kidney and heart. The specific methylation of the CpG dinucleotide at the USF-binding site impeded both the binding of USF and its transcriptional activation of the HP-27 gene. Chromatin immunoprecipitation using anti-USF antibodies revealed that USF bound to the HP-27 gene promoter in the liver, but not in the kidney or heart. Thus CpG methylation at the USF-binding site functions in establishing and maintaining tissue-specific transcription from the CpG-poor HP-27 gene promoter.

Preparing for winter: divergence in the summer-autumn hematological profiles from representative species of the squirrel family

We examined hematological parameters in four related sciurid species in the late summer-autumn to assess the role of habitat, elevation, body size, and behavior in shaping these parameters. Red squirrels (Tamiasciurus hudsonicus) and Arctic ground squirrels (Spermophilus parryii) were sampled in southwestern Yukon, yellow-pine chipmunks (Tamias amoenus) in southern Alberta, and the eastern grey squirrel (Sciurus carolinensis) in southern Ontario. We obtained whole blood samples from each species and compared glucose levels, red blood cell characteristics (hematocrit, red blood cell count, hemoglobin concentration, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration), and white blood cell counts (neutrophils, lymphocytes, monocytes, eosinophils, basophils) across species. We found species differences in glucose and red blood cell characteristics that may be a function of activity levels, phylogeny, or elevation, but not of body size, body condition, or adaptations to a semi-fossorial habitat. We also found species differences in white blood cell counts that remain unexplained by any single simple explanation and may be more useful for comparison of individuals within a given species than for interspecies comparisons.

HNF-1 regulates the promoter activity of the HP-27 gene

The hibernation-specific HP-27 gene is expressed specifically in the liver of the chipmunk, a hibernating species of the squirrel family, and exists as a pseudogene in the tree squirrel, a nonhibernating species. In the promoter region, the chipmunk gene has a potential HNF-1 binding site, and the tree squirrel gene has two base substitutions in the corresponding sequence. In this paper, we investigated the role of HNF-1 in the HP-27 gene promoter activity. Gel retardation assays with in vitro-translated HNF-1 and super-shift assays using HepG2 nuclear extracts and an anti-HNF-1 antibody revealed that HNF-1 bound to the chipmunk gene sequence. HNF-1 also bound to the tree squirrel sequence, but with much lower affinity. In HepG2 cells, HNF-1 activated transcription from the chipmunk HP-27 gene, but not from the tree squirrel gene. In addition, the tree squirrel-type base substitutions in the HNF-1 binding site greatly reduced the promoter activity of the chipmunk HP-27 gene. These results indicate that HNF-1 is required for the promoter activity of the chipmunk HP-27 gene, and that the base substitutions in the HNF-1 binding site are involved in the lack of HP-27 gene expression in the tree squirrel.

Mammalian hibernation: cellular and molecular responses to depressed metabolism and low temperature

Mammalian hibernators undergo a remarkable phenotypic switch that involves profound changes in physiology, morphology, and behavior in response to periods of unfavorable environmental conditions. The ability to hibernate is found throughout the class Mammalia and appears to involve differential expression of genes common to all mammals, rather than the induction of novel gene products unique to the hibernating state. The hibernation season is characterized by extended bouts of torpor, during which minimal body temperature (Tb) can fall as low as -2.9 degrees C and metabolism can be reduced to 1% of euthermic rates. Many global biochemical and physiological processes exploit low temperatures to lower reaction rates but retain the ability to resume full activity upon rewarming. Other critical functions must continue at physiologically relevant levels during torpor and be precisely regulated even at Tb values near 0 degrees C. Research using new tools of molecular and cellular biology is beginning to reveal how hibernators survive repeated cycles of torpor and arousal during the hibernation season. Comprehensive approaches that exploit advances in genomic and proteomic technologies are needed to further define the differentially expressed genes that distinguish the summer euthermic from winter hibernating states. Detailed understanding of hibernation from the molecular to organismal levels should enable the translation of this information to the development of a variety of hypothermic and hypometabolic strategies to improve outcomes for human and animal health.