1
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Hunstiger M, Johannsen MM, Oliver SR. Non-shivering thermogenesis is differentially regulated during the hibernation season in Arctic ground squirrels. Front Physiol 2023; 14:1207529. [PMID: 37520836 PMCID: PMC10372343 DOI: 10.3389/fphys.2023.1207529] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 06/22/2023] [Indexed: 08/01/2023] Open
Abstract
Arctic ground squirrels are small mammals that experience physiological extremes during the hibernation season. Body temperature rises from 1°C to 40°C during interbout arousal and requires tight thermoregulation to maintain rheostasis. Tissues from wild-caught Arctic ground squirrels were sampled over 9 months to assess the expression of proteins key to thermogenic regulation. Animals were sacrificed while aroused, and the extensor digitorum longus, diaphragm, brown adipose tissue, and white adipose tissue were probed using Western blots to assess protein expression and blood was sampled for metabolite analysis. Significant seasonal expression patterns emerged showing differential regulation. Contrary to our prediction, white adipose tissue showed no expression of uncoupling protein 1, but utilization of uncoupling protein 1 peaked in brown adipose tissue during the winter months and began to taper after terminal arousal in the spring. The opposite was true for muscular non-shivering thermogenesis. Sarco/endoplasmic reticulum calcium ATPase 1a and 2a expressions were depressed during the late hibernation season and rebounded after terminal arousal in diaphragm tissues, but only SERCA2a was differentially expressed in the extensor digitorum longus. The uncoupler, sarcolipin, was only detected in diaphragm samples and had a decreased expression during hibernation. The differential timing of these non-shivering pathways indicated distinct functions in maintaining thermogenesis which may depend on burrow temperature, availability of endogenous resources, and other seasonal activity demands on these tissues. These results could be impacted by fiber type makeup of the muscles collected, the body weight of the animal, and the date of entrance or exit from hibernation.
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Affiliation(s)
- Moriah Hunstiger
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK, United States
| | - Michelle Marie Johannsen
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK, United States
- Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK, United States
| | - S. Ryan Oliver
- Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK, United States
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2
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Repeated short excursions from thermoneutrality suffice to restructure brown adipose tissue. Biochimie 2023:S0300-9084(23)00006-8. [PMID: 36657658 DOI: 10.1016/j.biochi.2023.01.006] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 12/20/2022] [Accepted: 01/10/2023] [Indexed: 01/18/2023]
Abstract
Given the presence of brown adipose tissue in adult humans, an important issue is whether human brown adipose tissue is recruitable. Cold exposure is the canonical recruitment treatment; however, in experimental animals (mice), recruitment of brown adipose tissue is normally induced by placing the mice in constant cold, a procedure not feasible in humans. For possible translational applications, we have therefore investigated whether shorter daily excursions from thermoneutrality would suffice to qualitatively and quantitatively induce recruitment in mice. Mice, housed at thermoneutrality (30 °C) to mimic human conditions, were transferred every day for 4 weeks to cool conditions (18 °C), for 0, 15, 30, 120 and 420 min (or placed constantly in 18 °C). On the examination day, the mice were not exposed to cold. Very short daily exposures (≤30 min) were sufficient to induce structural changes in the form of higher protein density in brown adipose tissue, changes that may affect the identification of the tissue in e.g. computer tomography and other scan studies. To estimate thermogenic capacity, UCP1 protein levels were followed. No UCP1 protein was detectable in inguinal white adipose tissue. In the interscapular brown adipose tissue, a remarkable two-phase reaction was seen. Very short daily exposures (≤30 min) were sufficient to induce a significant increase in total UCP1 levels. For attainment of full cold acclimation, the mice had, however, to remain exposed to the cold. The studies indicate that marked alterations in brown adipose tissue composition can be induced in mammals through relatively modest stimulation events.
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3
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Sullivan IR, Adams DM, Greville LJS, Faure PA, Wilkinson GS. Big brown bats experience slower epigenetic ageing during hibernation. Proc Biol Sci 2022; 289:20220635. [PMID: 35946154 PMCID: PMC9364000 DOI: 10.1098/rspb.2022.0635] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Comparative analyses of bats indicate that hibernation is associated with increased longevity among species. However, it is not yet known if hibernation affects biological ageing of individuals. Here, we use DNA methylation (DNAm) as an epigenetic biomarker of ageing to determine the effect of hibernation on the big brown bat, Eptesicus fuscus. First, we compare epigenetic age, as predicted by a multi-species epigenetic clock, between hibernating and non-hibernating animals and find that hibernation is associated with epigenetic age. Second, we identify genomic sites that exhibit hibernation-associated change in DNAm, independent of age, by comparing samples taken from the same individual in hibernating and active seasons. This paired comparison identified over 3000 differentially methylated positions (DMPs) in the genome. Genome-wide association comparisons to tissue-specific functional elements reveals that DMPs with elevated DNAm during winter occur at sites enriched for quiescent chromatin states, whereas DMPs with reduced DNAm during winter occur at sites enriched for transcription enhancers. Furthermore, genes nearest DMPs are involved in regulation of metabolic processes and innate immunity. Finally, significant overlap exists between genes nearest hibernation DMPs and genes nearest previously identified longevity DMPs. Taken together, these results are consistent with hibernation influencing ageing and longevity in bats.
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Affiliation(s)
- Isabel R. Sullivan
- Department of Biology, University of Maryland, College Park, MD 20742, USA
| | - Danielle M. Adams
- Department of Biology, University of Maryland, College Park, MD 20742, USA,Department of Biological Sciences, Towson University, Towson, MD 21252, USA
| | - Lucas J. S. Greville
- Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, ON, Canada L8S 4K1,Department of Biology, University of Waterloo, Waterloo, ON, Canada N3 L 3G1
| | - Paul A. Faure
- Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, ON, Canada L8S 4K1
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4
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A critique on the theory of homeostasis. Physiol Behav 2022; 247:113712. [DOI: 10.1016/j.physbeh.2022.113712] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2021] [Revised: 01/17/2022] [Accepted: 01/19/2022] [Indexed: 01/27/2023]
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5
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Watts AJ, Logan SM, Kübber-Heiss A, Posautz A, Stalder G, Painer J, Gasch K, Giroud S, Storey KB. Regulation of Peroxisome Proliferator-Activated Receptor Pathway During Torpor in the Garden Dormouse, Eliomys quercinus. Front Physiol 2020; 11:615025. [PMID: 33408645 PMCID: PMC7779809 DOI: 10.3389/fphys.2020.615025] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 12/03/2020] [Indexed: 11/16/2022] Open
Abstract
Differential levels of n-6 and n-3 essential polyunsaturated fatty acids (PUFAs) are incorporated into the hibernator’s diet in the fall season preceding prolonged, multi-days bouts of torpor, known as hibernation. Peroxisome proliferator-activated receptor (PPAR) transcriptional activators bind lipids and regulate genes involved in fatty acid transport, beta-oxidation, ketogenesis, and insulin sensitivity; essential processes for survival during torpor. Thus, the DNA-binding activity of PPARα, PPARδ, PPARγ, as well as the levels of PPARγ coactivator 1α (PGC-1α) and L-fatty acid binding protein (L-FABP) were investigated in the hibernating garden dormouse (Eliomys quercinus). We found that dormice were hibernating in a similar way regardless of the n-6/n-3 PUFA diets fed to the animals during the fattening phase prior to hibernation. Further, metabolic rates and body mass loss during hibernation did not differ between dietary groups, despite marked differences in fatty acid profiles observed in white adipose tissue prior and at mid-hibernation. Overall, maintenance of PPAR DNA-binding activity was observed during torpor, and across three n-6/n-3 ratios, suggesting alternate mechanisms for the prioritization of lipid catabolism during torpor. Additionally, while no change was seen in L-FABP, significantly altered levels of PGC-1α were observed within the white adipose tissue and likely contributes to enhanced lipid metabolism when the diet favors n-6 PUFAs, i.e., high n-6/n-3 ratio, in both the torpid and euthermic state. Altogether, the maintenance of lipid metabolism during torpor makes it likely that consistent activity or levels of the investigated proteins are in aid of this metabolic profile.
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Affiliation(s)
| | | | - Anna Kübber-Heiss
- Department of Interdisciplinary Life Sciences, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Annika Posautz
- Department of Interdisciplinary Life Sciences, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Gabrielle Stalder
- Department of Interdisciplinary Life Sciences, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Johanna Painer
- Department of Interdisciplinary Life Sciences, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Kristina Gasch
- Department of Interdisciplinary Life Sciences, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Vienna, Austria
| | - Sylvain Giroud
- Department of Interdisciplinary Life Sciences, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Vienna, Austria
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6
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A comparative genomics multitool for scientific discovery and conservation. Nature 2020; 587:240-245. [PMID: 33177664 PMCID: PMC7759459 DOI: 10.1038/s41586-020-2876-6] [Citation(s) in RCA: 162] [Impact Index Per Article: 40.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2019] [Accepted: 07/27/2020] [Indexed: 12/11/2022]
Abstract
The Zoonomia Project is investigating the genomics of shared and specialized traits in eutherian mammals. Here we provide genome assemblies for 131 species, of which all but 9 are previously uncharacterized, and describe a whole-genome alignment of 240 species of considerable phylogenetic diversity, comprising representatives from more than 80% of mammalian families. We find that regions of reduced genetic diversity are more abundant in species at a high risk of extinction, discern signals of evolutionary selection at high resolution and provide insights from individual reference genomes. By prioritizing phylogenetic diversity and making data available quickly and without restriction, the Zoonomia Project aims to support biological discovery, medical research and the conservation of biodiversity. A whole-genome alignment of 240 phylogenetically diverse species of eutherian mammal—including 131 previously uncharacterized species—from the Zoonomia Project provides data that support biological discovery, medical research and conservation.
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7
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Miyazaki M, Shimozuru M, Tsubota T. Skeletal muscles of hibernating black bears show minimal atrophy and phenotype shifting despite prolonged physical inactivity and starvation. PLoS One 2019; 14:e0215489. [PMID: 30998788 PMCID: PMC6472773 DOI: 10.1371/journal.pone.0215489] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2018] [Accepted: 04/02/2019] [Indexed: 02/08/2023] Open
Abstract
Hibernating mammals experience prolonged periods of torpor and starvation during winter for up to 5–7 months. Though physical inactivity and malnutrition generally lead to profound loss of muscle mass and metabolic dysfunction in humans, hibernating bears show limited muscle atrophy and can successfully maintain locomotive function. These physiological features in bears allow us to hypothesize that hibernating bears uniquely alter the regulation of protein and energy metabolism in skeletal muscle which then contributes to “muscle atrophy resistance” against continued physical inactivity. In this study, alteration of signaling pathways governing protein and energy metabolisms was examined in skeletal muscle of the Japanese black bear (Ursus thibetanus japonicus). Sartorius muscle samples were collected from bear legs during late November (pre-hibernation) and early April (post-hibernation). Protein degradation pathways, through a ubiquitin-proteasome system (as assessed by increased expression of murf1 mRNA) and an autophagy-dependent system (as assessed by increased expression of atg7, beclin1, and map1lc3 mRNAs), were significantly activated in skeletal muscle following hibernation. In contrast, as indicated by a significant increase in S6K1 phosphorylation, an activation state of mTOR (mammalian/mechanistic target of rapamycin), which functions as a central regulator of protein synthesis, increased in post-hibernation samples. Gene expression of myostatin, a negative regulator of skeletal muscle mass, was significantly decreased post-hibernation. We also confirmed that the phenotype shifted toward slow-oxidative muscle and mitochondrial biogenesis. These observations suggest that protein and energy metabolism may be altered in skeletal muscle of hibernating bears, which then may contribute to limited loss of muscle mass and efficient energy utilization.
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Affiliation(s)
- Mitsunori Miyazaki
- Department of Physical Therapy, School of Rehabilitation Sciences, Health Sciences University of Hokkaido, Hokkaido, Japan
- * E-mail:
| | - Michito Shimozuru
- Laboratory of Wildlife Biology and Medicine, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido, Japan
| | - Toshio Tsubota
- Laboratory of Wildlife Biology and Medicine, Graduate School of Veterinary Medicine, Hokkaido University, Hokkaido, Japan
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8
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Regan MD, Chiang E, Martin SL, Porter WP, Assadi-Porter FM, Carey HV. Shifts in metabolic fuel use coincide with maximal rates of ventilation and body surface rewarming in an arousing hibernator. Am J Physiol Regul Integr Comp Physiol 2019; 316:R764-R775. [PMID: 30969844 DOI: 10.1152/ajpregu.00379.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
It is well established that hibernating mammals rely predominantly on lipid stores to fuel metabolism throughout the hibernation season. However, it is unclear if other endogenous fuels contribute to the rapid, ~400-fold increase in metabolic rate during the early phase of arousal from torpor. To investigate this issue, we used cavity ring-down spectroscopy, a technique that provides a real-time indication of fuel use by measuring the ratio of 13C to 12C in the exhaled CO2 of arousing 13-lined ground squirrels (Ictidomys tridecemlineatus). We used infrared thermography to simultaneously measure ventilation and surface temperature change in various body regions, and we interpreted these data in light of changing plasma metabolite abundances at multiple stages of arousal from torpor. We found that hibernating squirrels use a combination of lipids and, likely, carbohydrates to fuel the initial ~60 min of arousal before switching to predominantly lipid oxidation. This fuel switch coincided with times of maximal rates of ventilation and rewarming of different body surface regions, including brown adipose tissue. Infrared thermography revealed zonal rewarming, whereby the brown adipose tissue region was the first to warm, followed by the thoracic and head regions and, finally, the posterior half of the body. Consistent with the results from cavity ring-down spectroscopy, plasma metabolite dynamics during early arousal suggested a large reliance on fatty acids, with a contribution from carbohydrates and glycerol. Because of their high oxidative flux rates and efficient O2 use, carbohydrates might be an advantageous metabolic fuel during the early phase of arousal, when metabolic demands are high but ventilation rates and, thus, O2 supply are relatively low.
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Affiliation(s)
- Matthew D Regan
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin
| | - Edna Chiang
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin.,Department of Bacteriology, University of Wisconsin-Madison , Madison, Wisconsin
| | - Sandra L Martin
- Department of Cell and Developmental Biology, University of Colorado School of Medicine , Aurora, Colorado
| | - Warren P Porter
- Deparment of Integrative Biology, University of Wisconsin-Madison , Madison, Wisconsin
| | - Fariba M Assadi-Porter
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin.,Deparment of Integrative Biology, University of Wisconsin-Madison , Madison, Wisconsin
| | - Hannah V Carey
- Department of Comparative Biosciences, University of Wisconsin-Madison , Madison, Wisconsin
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9
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Gehrke S, Rice S, Stefanoni D, Wilkerson RB, Nemkov T, Reisz JA, Hansen KC, Lucas A, Cabrales P, Drew K, D'Alessandro A. Red Blood Cell Metabolic Responses to Torpor and Arousal in the Hibernator Arctic Ground Squirrel. J Proteome Res 2019; 18:1827-1841. [PMID: 30793910 DOI: 10.1021/acs.jproteome.9b00018] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Arctic ground squirrels provide a unique model to investigate metabolic responses to hibernation in mammals. During winter months these rodents are exposed to severe hypothermia, prolonged fasting, and hypoxemia. In the light of their role in oxygen transport/off-loading and owing to the absence of nuclei and organelles (and thus de novo protein synthesis capacity), mature red blood cells have evolved metabolic programs to counteract physiological or pathological hypoxemia. However, red blood cell metabolism in hibernation has not yet been investigated. Here we employed targeted and untargeted metabolomics approaches to investigate erythrocyte metabolism during entrance to torpor to arousal, with a high resolution of the intermediate time points. We report that torpor and arousal promote metabolism through glycolysis and pentose phosphate pathway, respectively, consistent with previous models of oxygen-dependent metabolic modulation in mature erythrocytes. Erythrocytes from hibernating squirrels showed up to 100-fold lower levels of biomarkers of reperfusion injury, such as the pro-inflammatory dicarboxylate succinate. Altered tryptophan metabolism during torpor was here correlated to the accumulation of potentially neurotoxic catabolites kynurenine, quinolinate, and picolinate. Arousal was accompanied by alterations of sulfur metabolism, including sudden spikes in a metabolite putatively identified as thiorphan (level 1 confidence)-a potent inhibitor of several metalloproteases that play a crucial role in nociception and inflammatory complication to reperfusion secondary to ischemia or hemorrhage. Preliminary studies in rats showed that intravenous injection of thiorphan prior to resuscitation mitigates metabolic and cytokine markers of reperfusion injury, etiological contributors to inflammatory complications after shock.
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Affiliation(s)
- Sarah Gehrke
- Department of Biochemistry and Molecular Genetics , University of Colorado Denver - Anschutz Medical Campus , Aurora , Colorado 80045 , United States
| | - Sarah Rice
- Department of Chemistry and Biochemistry , University of Alaska Fairbanks , Fairbanks , Alaska 99775 , United States
| | - Davide Stefanoni
- Department of Biochemistry and Molecular Genetics , University of Colorado Denver - Anschutz Medical Campus , Aurora , Colorado 80045 , United States
| | - Rebecca B Wilkerson
- Department of Biochemistry and Molecular Genetics , University of Colorado Denver - Anschutz Medical Campus , Aurora , Colorado 80045 , United States
| | - Travis Nemkov
- Department of Biochemistry and Molecular Genetics , University of Colorado Denver - Anschutz Medical Campus , Aurora , Colorado 80045 , United States
| | - Julie A Reisz
- Department of Biochemistry and Molecular Genetics , University of Colorado Denver - Anschutz Medical Campus , Aurora , Colorado 80045 , United States
| | - Kirk C Hansen
- Department of Biochemistry and Molecular Genetics , University of Colorado Denver - Anschutz Medical Campus , Aurora , Colorado 80045 , United States
| | - Alfredo Lucas
- Department of Bioengineering , University of California San Diego , La Jolla , California 92093 , United States
| | - Pedro Cabrales
- Department of Bioengineering , University of California San Diego , La Jolla , California 92093 , United States
| | - Kelly Drew
- Department of Chemistry and Biochemistry , University of Alaska Fairbanks , Fairbanks , Alaska 99775 , United States
| | - Angelo D'Alessandro
- Department of Biochemistry and Molecular Genetics , University of Colorado Denver - Anschutz Medical Campus , Aurora , Colorado 80045 , United States
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10
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MacCannell ADV, Sinclair KJ, Tattersall GJ, McKenzie CA, Staples JF. Identification of a lipid-rich depot in the orbital cavity of the thirteen-lined ground squirrel. ACTA ACUST UNITED AC 2019; 222:jeb.195750. [PMID: 30679243 DOI: 10.1242/jeb.195750] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2018] [Accepted: 01/16/2019] [Indexed: 12/28/2022]
Abstract
We discovered a previously undescribed orbital lipid depot in the thirteen-lined ground squirrel during the first ever magnetic resonance image (MRI) of this common experimental model of mammalian hibernation. In animals housed at constant ambient temperatures (5°C or 25°C, 12 h:12 h light:dark photoperiod), the volume of this depot increased in the autumn and decreased in the spring, suggesting an endogenous circannual pattern. Water-fat MRI revealed that throughout the year this depot is composed of ∼40% lipid, similar to brown adipose tissue (BAT). During arousal from torpor, thermal images showed higher surface temperatures near this depot before the rest of the head warmed, suggesting a thermoregulatory function. This depot, however, does not contain uncoupling protein 1, a BAT biomarker, or uncoupling protein 3. Histology shows blood vessels in close proximity to each other, suggesting it may serve as a vascular rete, perhaps to preferentially warm the eye and brain during arousals.
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Affiliation(s)
- Amanda D V MacCannell
- Department of Biology, University of Western Ontario, London, ON, N6A 5B8, Canada .,Discovery and Translational Science Department, University of Leeds, Leeds LS2 9DA, UK
| | - Kevin J Sinclair
- Department of Medical Biophysics, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Glenn J Tattersall
- Department of Biological Sciences, Brock University, St Catharines, ON, L2S 3A1, Canada
| | - Charles A McKenzie
- Department of Medical Biophysics, University of Western Ontario, London, ON, N6A 5B7, Canada
| | - James F Staples
- Department of Biology, University of Western Ontario, London, ON, N6A 5B8, Canada
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11
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Chayama Y, Ando L, Sato Y, Shigenobu S, Anegawa D, Fujimoto T, Taii H, Tamura Y, Miura M, Yamaguchi Y. Molecular Basis of White Adipose Tissue Remodeling That Precedes and Coincides With Hibernation in the Syrian Hamster, a Food-Storing Hibernator. Front Physiol 2019; 9:1973. [PMID: 30745884 PMCID: PMC6360343 DOI: 10.3389/fphys.2018.01973] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2018] [Accepted: 12/31/2018] [Indexed: 12/31/2022] Open
Abstract
Mammalian hibernators store fat extensively in white adipose tissues (WATs) during pre-hibernation period (Pre-HIB) to prepare for hibernation. However, the molecular mechanisms underlying the pre-hibernation remodeling of WAT have not been fully elucidated. Syrian hamsters, a food-storing hibernator, can hibernate when exposed to a winter-like short day photoperiod and cold ambient temperature (SD-Cold). Animals subjected to prolonged SD-Cold had smaller white adipocytes and beige-like cells within subcutaneous inguinal WAT (iWAT). Time-course analysis of gene expression with RNA-sequencing and quantitative PCR demonstrated that the mRNA expression of not only genes involved in lipid catabolism (lipolysis and beta-oxidation) but also lipid anabolism (lipogenesis and lipid desaturation) was simultaneously up-regulated prior to hibernation onset in the animals. The enhanced capacity of both lipid catabolism and lipid anabolism during hibernation period (HIB) is striking contrast to previous observations in fat-storing hibernators that only enhance catabolism during HIB. The mRNA expression of mTORC1 and PPAR signaling molecules increased, and pharmacological activation of PPARs indeed up-regulated lipid metabolism genes in iWAT explants from Syrian hamsters. These results suggest that the Syrian hamster rewires lipid metabolisms while preparing for hibernation to effectively utilize body fat and synthesize it from food intake during HIB.
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Affiliation(s)
- Yuichi Chayama
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Lisa Ando
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Yuya Sato
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Shuji Shigenobu
- Functional Genomics Facility, National Institute for Basic Biology, Okazaki, Japan
| | - Daisuke Anegawa
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Takayuki Fujimoto
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Hiroki Taii
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Yutaka Tamura
- Department of Pharmacology, Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University, Fukuyama, Japan
| | - Masayuki Miura
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan
| | - Yoshifumi Yamaguchi
- Department of Genetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan.,Hibernation Metabolism, Physiology and Development Group, Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan
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12
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Andrews MT. Molecular interactions underpinning the phenotype of hibernation in mammals. J Exp Biol 2019; 222:222/2/jeb160606. [DOI: 10.1242/jeb.160606] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
ABSTRACT
Mammals maintain a constant warm body temperature, facilitating a wide variety of metabolic reactions. Mammals that hibernate have the ability to slow their metabolism, which in turn reduces their body temperature and leads to a state of hypothermic torpor. For this metabolic rate reduction to occur on a whole-body scale, molecular interactions that change the physiology of cells, tissues and organs are required, resulting in a major departure from normal mammalian homeostasis. The aim of this Review is to cover recent advances in the molecular biology of mammalian hibernation, including the role of small molecules, seasonal changes in gene expression, cold-inducible RNA-binding proteins, the somatosensory system and emerging information on hibernating primates. To underscore the importance of differential gene expression across the hibernation cycle, mRNA levels for 14,261 ground squirrel genes during periods of activity and torpor are made available for several tissues via an interactive transcriptome browser. This Review also addresses recent findings on molecular interactions responsible for multi-day survival of near-freezing body temperatures, single-digit heart rates and a slowed metabolism that greatly reduces oxygen consumption. A better understanding of how natural hibernators survive these physiological extremes is beginning to lead to innovations in human medicine.
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Affiliation(s)
- Matthew T. Andrews
- Department of Biochemistry and Biophysics, Oregon State University, Corvallis, OR 97331, USA
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13
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Sprenger RJ, Tanumihardjo SA, Kurtz CC. Developing a Model of Vitamin A Deficiency in a Hibernating Mammal, the 13-Lined Ground Squirrel ( Ictidomys tridecemlineatus). Comp Med 2018; 68:196-203. [PMID: 29801522 DOI: 10.30802/aalas-cm-17-000113] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Retinoic acid, a bioactive metabolite of vitamin A, plays key roles in immune function and vision and adipose tissue development. Our goal was to study the effect of vitamin A deficiency in physiologic changes seen in hibernating 13-lined ground squirrels (Ictidomys tridecemlineatus). In this study, we first developed a model of vitamin A deficiency that was based on published mouse models; we then examined the role of RA in the circannual cycle of and adipose accumulation in this hibernating species. Gravid female ground squirrels began consuming a deficient diet during the last 2 wk of their 4-wk gestation; pups received the diet until they were 8 wk old, when severe symptoms of hypovitaminosis were observed, requiring the animals' removal from the protocol. Body size and adipose mass were significantly lower in vitamin-deficient pups than controls. To avoid these complications, we developed a second model, in which pups started on the deficient diet after weaning. The revised model produced few symptoms of deficiency, and squirrels were able to remain on the diet through spring emergence. Liver retinol analysis showed that deficient squirrels essentially had no vitamin A stores. Our data suggest that 13-lined ground squirrels maintain higher concentrations of stored retinol than other rodent species, such that their dietary needs may differ from those of traditional laboratory rodent models. Our results indicate that ground squirrels are especially susceptible to vitamin A deficiency, and ground squirrels should not be fed a deficient diet until after weaning, to avoid severe symptoms. Interestingly, vitamin A deficiency does not seem to affect this species' ability to hibernate successfully.
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Affiliation(s)
- Ryan J Sprenger
- Department of Biology, University of Wisconsin-Oshkosh, Oshkosh, Wisconsin, USA
| | | | - Courtney C Kurtz
- Department of Biology, University of Wisconsin-Oshkosh, Oshkosh, Wisconsin, USA.
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14
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Ballinger MA, Andrews MT. Nature's fat-burning machine: brown adipose tissue in a hibernating mammal. ACTA ACUST UNITED AC 2018. [PMID: 29514878 DOI: 10.1242/jeb.162586] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Brown adipose tissue (BAT) is a unique thermogenic tissue in mammals that rapidly produces heat via nonshivering thermogenesis. Small mammalian hibernators have evolved the greatest capacity for BAT because they use it to rewarm from hypothermic torpor numerous times throughout the hibernation season. Although hibernator BAT physiology has been investigated for decades, recent efforts have been directed toward understanding the molecular underpinnings of BAT regulation and function using a variety of methods, from mitochondrial functional assays to 'omics' approaches. As a result, the inner-workings of hibernator BAT are now being illuminated. In this Review, we discuss recent research progress that has identified players and pathways involved in brown adipocyte differentiation and maturation, as well as those involved in metabolic regulation. The unique phenotype of hibernation, and its reliance on BAT to generate heat to arouse mammals from torpor, has uncovered new molecular mechanisms and potential strategies for biomedical applications.
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Affiliation(s)
- Mallory A Ballinger
- Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720, USA
| | - Matthew T Andrews
- Department of Biochemistry and Biophysics, Oregon State University, Corvallis, OR 97331, USA
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15
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MacCannell ADV, Jackson EC, Mathers KE, Staples JF. An improved method for detecting torpor entrance and arousal in a mammalian hibernator using heart rate data. ACTA ACUST UNITED AC 2018; 221:jeb.174508. [PMID: 29361606 DOI: 10.1242/jeb.174508] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2017] [Accepted: 01/10/2018] [Indexed: 12/22/2022]
Abstract
We used electrocardiogram (ECG) telemeters to measure the heart rate of hibernating Ictidomys tridecemlineatus (thirteen-lined ground squirrel). An increase in heart rate from 2.2 to 5 beats min-1 accurately identified arousal from torpor before any change in body temperature was detected. Variability in raw heart rate data was significantly reduced by a forward-backward Butterworth low-pass filter, allowing for discrete differential analysis. A decrease in filtered heart rate to 70% of maximum values in interbout euthermia (from approximately 312 to 235 beats min-1) accurately detected entrance into torpor bouts. At this point, body temperature had fallen from 36.1°C to only 34.7°C, much higher than the 30°C typically used to identify entrance. Using these heart rate criteria allowed advanced detection of entrance and arousal (detected 51.9 and 76 min earlier, respectively), compared with traditional body temperature criteria. This method will improve our ability to detect biochemical and molecular markers underlying these transition periods, during which many physiological changes occur.
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Affiliation(s)
| | - Ethan C Jackson
- Department of Computer Science, University of Western Ontario, London ON, N6A5B7, Canada
| | - Katherine E Mathers
- Department of Biology, University of Western Ontario, London ON, N6A5B8, Canada
| | - James F Staples
- Department of Biology, University of Western Ontario, London ON, N6A5B8, Canada
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16
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MacCannell ADV, Sinclair KJ, McKenzie CA, Staples JF. Environmental temperature effects on adipose tissue growth in a hibernator. J Exp Biol 2018; 222:jeb.194548. [DOI: 10.1242/jeb.194548] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2018] [Accepted: 12/12/2018] [Indexed: 12/21/2022]
Abstract
Obligate hibernators express circannual patterns of body mass and hibernation, which persist under constant laboratory conditions. Brown Adipose Tissue (BAT) is important for thermogenesis during arousals from hibernation, whereas White Adipose Tissue (WAT) serves as energy storage and thermal insulation. The goal of this study was to investigate the effects of environmental temperature on BAT and WAT. We hypothesized that changes to environmental temperature would not influence the pattern of mass gain or BAT and WAT volume in the thirteen-lined ground squirrel (Ictidomys tridecemlineatus). To test this, we housed animals thermoneutral 25°C (warm-housed) or 5°C (cold-housed), with the same photoperiod (12 h light:12 h dark) over an entire year. Throughout the year we measured the volume and water-fat ratio of WAT and BAT using magnetic resonance imaging (MRI). We found no evidence of torpor in the warm-housed animals, indicating that this species might not be an obligate hibernator, as previously assumed. Regardless of ambient temperature BAT volume increased prior to winter, then decreased in late winter with no change in water-fat ratio. By contrast both body mass and WAT volume of cold-housed animals declined throughout the winter and recovered after hibernation, but thermoneutral housing produced no circannual pattern in body mass, even though WAT volume declined in late winter. Cold exposure appears to be a primary regulator for WAT but BAT may exhibit an endogenous circannual rhythm in terms of depot volume.
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Affiliation(s)
- Amanda D. V. MacCannell
- Dept. of Biology, University of Western Ontario, London ON, N6A5B8, Canada
- Current address: Discovery and Translational Science Dept., University of Leeds, Leeds, LS29JT, UK
| | - Kevin J. Sinclair
- Dept. of Medical Biophysics, University of Western Ontario, London ON, N6A5B7, Canada
| | - Charles A. McKenzie
- Dept. of Medical Biophysics, University of Western Ontario, London ON, N6A5B7, Canada
| | - James F. Staples
- Dept. of Biology, University of Western Ontario, London ON, N6A5B8, Canada
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17
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Herinckx G, Hussain N, Opperdoes FR, Storey KB, Rider MH, Vertommen D. Changes in the phosphoproteome of brown adipose tissue during hibernation in the ground squirrel, Ictidomys tridecemlineatus. Physiol Genomics 2017; 49:462-472. [PMID: 28698229 DOI: 10.1152/physiolgenomics.00038.2017] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2017] [Revised: 07/06/2017] [Accepted: 07/06/2017] [Indexed: 11/22/2022] Open
Abstract
Mammalian hibernation is characterized by metabolic rate depression and a strong decrease in core body temperature that together create energy savings such that most species do not have to eat over the winter months. Brown adipose tissue (BAT), a thermogenic tissue that uses uncoupled mitochondrial respiration to generate heat instead of ATP, plays a major role in rewarming from deep torpor. In the present study we developed a label-free liquid chromatography mass spectrometry (LC-MS) strategy to investigate both differential protein expression and protein phosphorylation in BAT extracts from euthermic vs. hibernating ground squirrels (Ictidomys tridecemlineatus). In particular, we incorporated the filter-assisted sample preparation protocol, which provides a more in-depth analysis compared with gel-based and other LC-MS proteomics approaches. Surprisingly, mitochondrial membrane and matrix protein expression in BAT was largely constant between active euthermic squirrels and their hibernating counterparts. Validation by immunoblotting confirmed that the protein levels of mitochondrial respiratory chain complexes were largely unchanged in hibernating vs. euthermic animals. On the other hand, phosphoproteomics revealed that pyruvate dehydrogenase (PDH) phosphorylation increased during squirrel hibernation, confirmed by immunoblotting with phospho-specific antibodies. PDH phosphorylation leads to its inactivation, which suggests that BAT carbohydrate oxidation is inhibited during hibernation. Phosphorylation of hormone-sensitive lipase (HSL) was also found to increase during hibernation, suggesting that HSL would be active in BAT to produce the fatty acids that are likely the primary fuel for thermogenesis upon arousal. Increased perilipin phosphorylation along with that of a number of other proteins was also revealed, emphasizing the importance of protein phosphorylation as a regulatory mechanism during mammalian hibernation.
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Affiliation(s)
- Gaëtan Herinckx
- de Duve Institute, Université catholique de Louvain, Brussels, Belgium; and
| | - Nusrat Hussain
- de Duve Institute, Université catholique de Louvain, Brussels, Belgium; and
| | - Fred R Opperdoes
- de Duve Institute, Université catholique de Louvain, Brussels, Belgium; and
| | - Kenneth B Storey
- Institute of Biochemistry and Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Mark H Rider
- de Duve Institute, Université catholique de Louvain, Brussels, Belgium; and
| | - Didier Vertommen
- de Duve Institute, Université catholique de Louvain, Brussels, Belgium; and
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18
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Tupone D, Cano G, Morrison SF. Thermoregulatory inversion: a novel thermoregulatory paradigm. Am J Physiol Regul Integr Comp Physiol 2017; 312:R779-R786. [PMID: 28330964 DOI: 10.1152/ajpregu.00022.2017] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Revised: 03/01/2017] [Accepted: 03/15/2017] [Indexed: 01/06/2023]
Abstract
To maintain core body temperature in mammals, the normal central nervous system (CNS) thermoregulatory reflex networks produce an increase in brown adipose tissue (BAT) thermogenesis in response to skin cooling and an inhibition of the sympathetic outflow to BAT during skin rewarming. In contrast, these normal thermoregulatory reflexes appear to be inverted in hibernation/torpor; thermogenesis is inhibited during exposure to a cold environment, allowing dramatic reductions in core temperature and metabolism, and thermogenesis is activated during skin rewarming, contributing to a return of normal body temperature. Here, we describe two unrelated experimental paradigms in which rats, a nonhibernating/torpid species, exhibit a "thermoregulatory inversion," which is characterized by an inhibition of BAT thermogenesis in response to skin cooling, and a switch in the gain of the skin cooling reflex transfer function from negative to positive values. Either transection of the neuraxis immediately rostral to the dorsomedial hypothalamus in anesthetized rats or activation of A1 adenosine receptors within the CNS of free-behaving rats produces a state of thermoregulatory inversion in which skin cooling inhibits BAT thermogenesis, leading to hypothermia, and skin warming activates BAT, supporting an increase in core temperature. These results reflect the existence of a novel neural circuit that mediates inverted thermoregulatory reflexes and suggests a pharmacological mechanism through which a deeply hypothermic state can be achieved in nonhibernating/torpid mammals, possibly including humans.
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Affiliation(s)
- Domenico Tupone
- Department of Neurological Surgery, Oregon Health and Science University, Portland, Oregon; and
| | - Georgina Cano
- Department of Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania
| | - Shaun F Morrison
- Department of Neurological Surgery, Oregon Health and Science University, Portland, Oregon; and
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19
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MacCannell A, Sinclair K, Friesen-Waldner L, McKenzie CA, Staples JF. Water-fat MRI in a hibernator reveals seasonal growth of white and brown adipose tissue without cold exposure. J Comp Physiol B 2017; 187:759-767. [PMID: 28324157 DOI: 10.1007/s00360-017-1075-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 12/13/2016] [Accepted: 02/26/2017] [Indexed: 11/24/2022]
Abstract
Obligate hibernators, such as ground squirrels, display circannual patterns which persist even under constant laboratory conditions, suggesting that they are regulated by endogenous rhythms. Brown adipose tissue (BAT) is important for thermogenesis during periodic arousals from hibernation when core body temperature rises spontaneously from 5 to 37 °C. In most small eutherians BAT growth requires several weeks of cold exposure. We hypothesized that in the thirteen-lined ground squirrel (Ictidomys tridecemlineatus), a hibernator, BAT growth is regulated, in part, by an endogenous rhythm and we predicted that this growth would precede the hibernation season without cold exposure. We tested this prediction using repeated water-fat magnetic resonance imaging over a year, including the hibernation season. Thoracic BAT depots increased in volume from spring through autumn even though animals were housed at ~22 °C. Subsequent cold exposure (5 °C) enlarged the thoracic BAT further. The fat fraction of this tissue fell significantly during the period of peak growth, indicating relative increases in non-triglyceride components, perhaps mitochondria or vasculature. We also found that the proportion of the body consisting of white adipose tissue (WAT) increased steadily from spring through autumn, and fell throughout hibernation, mirroring changes in body mass. Unlike BAT, WAT fat fractions remained constant (near 90%) throughout the year. Future studies will evaluate the significance of photoperiod and cold exposure on the growth of these tissues. We also found tissue with a fat fraction characteristic of BAT in the head near the eyes, a potentially novel discovery that requires further confirmation.
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Affiliation(s)
- Amanda MacCannell
- Department of Biology, University of Western Ontario, London, ON, N6A 5B8, Canada
| | - Kevin Sinclair
- Medical Biophysics, University of Western Ontario, London, ON, N6A 5B8, Canada
| | | | - Charles A McKenzie
- Medical Biophysics, University of Western Ontario, London, ON, N6A 5B8, Canada
| | - James F Staples
- Department of Biology, University of Western Ontario, London, ON, N6A 5B8, Canada.
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20
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Ballinger MA, Schwartz C, Andrews MT. Enhanced oxidative capacity of ground squirrel brain mitochondria during hibernation. Am J Physiol Regul Integr Comp Physiol 2017; 312:R301-R310. [PMID: 28077389 DOI: 10.1152/ajpregu.00314.2016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 01/06/2017] [Accepted: 01/08/2017] [Indexed: 11/22/2022]
Abstract
During hibernation, thirteen-lined ground squirrels (Ictidomys tridecemlineatus) regularly cycle between bouts of torpor and interbout arousal (IBA). Most of the brain is electrically quiescent during torpor but regains activity quickly upon arousal to IBA, resulting in extreme oscillations in energy demand during hibernation. We predicted increased functional capacity of brain mitochondria during hibernation compared with spring to accommodate the variable energy demands of hibernation. To address this hypothesis, we examined mitochondrial bioenergetics in the ground squirrel brain across three time points: spring (SP), torpor (TOR), and IBA. Respiration rates of isolated brain mitochondria through complex I of the electron transport chain were more than twofold higher in TOR and IBA than in SP (P < 0.05). We also found a 10% increase in membrane potential between hibernation and spring (P < 0.05), and that proton leak was lower in TOR and IBA than in SP. Finally, there was a 30% increase in calcium loading in SP brain mitochondria compared with TOR and IBA (P < 0.01). To analyze brain mitochondrial abundance between spring and hibernation, we measured the ratio of copy number in a mitochondrial gene (ND1) vs. a nuclear gene (B2M) in frozen cerebral cortex samples. No significant differences were observed in DNA copies between SP and IBA. These data show that brain mitochondrial bioenergetics are not static across the year and suggest that brain mitochondria function more effectively during the hibernation season, allowing for rapid production of energy to meet demand when extreme physiological changes are occurring.
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Affiliation(s)
- Mallory A Ballinger
- Department of Biology, University of Minnesota Duluth, Duluth, Minnesota; and
| | - Christine Schwartz
- Department of Biology, University of Minnesota Duluth, Duluth, Minnesota; and.,Department of Biology, University of Wisconsin-La Crosse, La Crosse, Wisconsin
| | - Matthew T Andrews
- Department of Biology, University of Minnesota Duluth, Duluth, Minnesota; and
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21
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McFarlane SV, Mathers KE, Staples JF. Reversible temperature-dependent differences in brown adipose tissue respiration during torpor in a mammalian hibernator. Am J Physiol Regul Integr Comp Physiol 2017; 312:R434-R442. [PMID: 28077390 DOI: 10.1152/ajpregu.00316.2016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2016] [Revised: 12/06/2016] [Accepted: 01/06/2017] [Indexed: 01/23/2023]
Abstract
Although seasonal modifications of brown adipose tissue (BAT) in hibernators are well documented, we know little about functional regulation of BAT in different phases of hibernation. In the 13-lined ground squirrel, liver mitochondrial respiration is suppressed by up to 70% during torpor. This suppression is reversed during arousal and interbout euthermia (IBE), and corresponds with patterns of maximal activities of electron transport system (ETS) enzymes. Uncoupling of BAT mitochondria is controlled by free fatty acid release stimulated by sympathetic activation of adipocytes, so we hypothesized that further regulation at the level of the ETS would be of little advantage. As predicted, maximal ETS enzyme activities of isolated BAT mitochondria did not differ between torpor and IBE. In contrast to this pattern, respiration rates of mitochondria isolated from torpid individuals were suppressed by ~60% compared with rates from IBE individuals when measured at 37°C. At 10°C, however, mitochondrial respiration rates tended to be greater in torpor than IBE. As a result, the temperature sensitivity (Q10) of mitochondrial respiration was significantly lower in torpor (~1.4) than IBE (~2.4), perhaps facilitating energy savings during entrance into torpor and thermogenesis at low body temperatures. Despite the observed differences in isolated mitochondria, norepinephrine-stimulated respiration rates of isolated BAT adipocytes did not differ between torpor and IBE, perhaps because the adipocyte isolation requires lengthy incubation at 37°C, potentially reversing any changes that occur in torpor. Such changes may include remodeling of BAT mitochondrial membrane phospholipids, which could change in situ enzyme activities and temperature sensitivities.
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Affiliation(s)
- Sarah V McFarlane
- Department of Biology, University of Western Ontario, London, Ontario, Canada
| | - Katherine E Mathers
- Department of Biology, University of Western Ontario, London, Ontario, Canada
| | - James F Staples
- Department of Biology, University of Western Ontario, London, Ontario, Canada
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22
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D'Alessandro A, Nemkov T, Bogren LK, Martin SL, Hansen KC. Comfortably Numb and Back: Plasma Metabolomics Reveals Biochemical Adaptations in the Hibernating 13-Lined Ground Squirrel. J Proteome Res 2016; 16:958-969. [PMID: 27991798 DOI: 10.1021/acs.jproteome.6b00884] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Hibernation is an evolutionary adaptation that affords some mammals the ability to exploit the cold to achieve extreme metabolic depression (torpor) while avoiding ischemia/reperfusion or hemorrhagic shock injuries. Hibernators cycle periodically out of torpor, restoring high metabolic activity. If understood at the molecular level, the adaptations underlying torpor-arousal cycles may be leveraged for translational applications in critical fields such as intensive care medicine. Here, we monitored 266 metabolites to investigate the metabolic adaptations to hibernation in plasma from 13-lined ground squirrels (57 animals, 9 time points). Results indicate that the periodic arousals foster the removal of potentially toxic oxidative stress-related metabolites, which accumulate in plasma during torpor while replenishing reservoirs of circulating catabolic substrates (free fatty acids and amino acids). Specifically, we identified metabolic fluctuations of basic amino acids lysine and arginine, one-carbon metabolism intermediates, and sulfur-containing metabolites methionine, cysteine, and cystathionine. Conversely, reperfusion injury markers such as succinate/fumarate remained relatively stable across cycles. Considering the cycles of these metabolites with the hibernator's cycling metabolic activity together with their well-established role as substrates for the production of hydrogen sulfide (H2S), we hypothesize that these metabolic fluctuations function as a biological clock regulating torpor to arousal transitions and resistance to reperfusion during arousal.
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Affiliation(s)
- Angelo D'Alessandro
- Department of Biochemistry and Molecular Genetics and ‡Department of Cell and Developmental Biology, University of Colorado Denver - Anschutz Medical Campus , Aurora, Colorado 80045, United States
| | - Travis Nemkov
- Department of Biochemistry and Molecular Genetics and ‡Department of Cell and Developmental Biology, University of Colorado Denver - Anschutz Medical Campus , Aurora, Colorado 80045, United States
| | - Lori K Bogren
- Department of Biochemistry and Molecular Genetics and ‡Department of Cell and Developmental Biology, University of Colorado Denver - Anschutz Medical Campus , Aurora, Colorado 80045, United States
| | - Sandra L Martin
- Department of Biochemistry and Molecular Genetics and ‡Department of Cell and Developmental Biology, University of Colorado Denver - Anschutz Medical Campus , Aurora, Colorado 80045, United States
| | - Kirk C Hansen
- Department of Biochemistry and Molecular Genetics and ‡Department of Cell and Developmental Biology, University of Colorado Denver - Anschutz Medical Campus , Aurora, Colorado 80045, United States
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23
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Ballinger MA, Hess C, Napolitano MW, Bjork JA, Andrews MT. Seasonal changes in brown adipose tissue mitochondria in a mammalian hibernator: from gene expression to function. Am J Physiol Regul Integr Comp Physiol 2016; 311:R325-36. [PMID: 27225952 DOI: 10.1152/ajpregu.00463.2015] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Accepted: 05/24/2016] [Indexed: 12/25/2022]
Abstract
Brown adipose tissue (BAT) is a thermogenic organ that is vital for hibernation in mammals. Throughout the hibernation season, BAT mitochondrial uncoupling protein 1 (UCP1) enables rapid rewarming from hypothermic torpor to periodic interbout arousals (IBAs), as energy is dissipated as heat. However, BAT's unique ability to rewarm the body via nonshivering thermogenesis is not necessary outside the hibernation season, suggesting a potential seasonal change in the regulation of BAT function. Here, we examined the BAT mitochondrial proteome and mitochondrial bioenergetics in the thirteen-lined ground squirrel (Ictidomys tridecemlineatus) across four time points: spring, fall, torpor, and IBA. Relative mitochondrial content of BAT was estimated by measuring BAT pad mass, UCP1 protein content, and mitochondrial DNA (mtDNA) copy number. BAT mtDNA content was significantly lower in spring compared with torpor and IBA (P < 0.05). UCP1 mRNA and protein levels were highest during torpor and IBA. Respiration rates of isolated BAT mitochondria were interrogated at each complex of the electron transport chain. Respiration at complex II was significantly higher in torpor and IBA compared with spring (P < 0.05), suggesting an enhancement in mitochondrial respiratory capacity during hibernation. Additionally, proteomic iTRAQ labeling identified 778 BAT mitochondrial proteins. Proteins required for mitochondrial lipid translocation and β-oxidation were upregulated during torpor and IBA and downregulated in spring. These data imply that BAT bioenergetics and mitochondrial content are not static across the year, despite the year-round presence of UCP1.
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Affiliation(s)
| | - Clair Hess
- Department of Biology, University of Minnesota Duluth, Duluth, Minnesota
| | - Max W Napolitano
- Department of Biology, University of Minnesota Duluth, Duluth, Minnesota
| | - James A Bjork
- Department of Biology, University of Minnesota Duluth, Duluth, Minnesota
| | - Matthew T Andrews
- Department of Biology, University of Minnesota Duluth, Duluth, Minnesota
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24
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Abstract
Extended bouts of fasting are ingrained in the ecology of many organisms, characterizing aspects of reproduction, development, hibernation, estivation, migration, and infrequent feeding habits. The challenge of long fasting episodes is the need to maintain physiological homeostasis while relying solely on endogenous resources. To meet that challenge, animals utilize an integrated repertoire of behavioral, physiological, and biochemical responses that reduce metabolic rates, maintain tissue structure and function, and thus enhance survival. We have synthesized in this review the integrative physiological, morphological, and biochemical responses, and their stages, that characterize natural fasting bouts. Underlying the capacity to survive extended fasts are behaviors and mechanisms that reduce metabolic expenditure and shift the dependency to lipid utilization. Hormonal regulation and immune capacity are altered by fasting; hormones that trigger digestion, elevate metabolism, and support immune performance become depressed, whereas hormones that enhance the utilization of endogenous substrates are elevated. The negative energy budget that accompanies fasting leads to the loss of body mass as fat stores are depleted and tissues undergo atrophy (i.e., loss of mass). Absolute rates of body mass loss scale allometrically among vertebrates. Tissues and organs vary in the degree of atrophy and downregulation of function, depending on the degree to which they are used during the fast. Fasting affects the population dynamics and activities of the gut microbiota, an interplay that impacts the host's fasting biology. Fasting-induced gene expression programs underlie the broad spectrum of integrated physiological mechanisms responsible for an animal's ability to survive long episodes of natural fasting.
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Affiliation(s)
- Stephen M Secor
- Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama, USA
| | - Hannah V Carey
- Department of Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, Wisconsin, USA
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25
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Abstract
Many environmental conditions can constrain the ability of animals to obtain sufficient food energy, or transform that food energy into useful chemical forms. To survive extended periods under such conditions animals must suppress metabolic rate to conserve energy, water, or oxygen. Amongst small endotherms, this metabolic suppression is accompanied by and, in some cases, facilitated by a decrease in core body temperature-hibernation or daily torpor-though significant metabolic suppression can be achieved even with only modest cooling. Within some ectotherms, winter metabolic suppression exceeds the passive effects of cooling. During dry seasons, estivating ectotherms can reduce metabolism without changes in body temperature, conserving energy reserves, and reducing gas exchange and its inevitable loss of water vapor. This overview explores the similarities and differences of metabolic suppression among these states within adult animals (excluding developmental diapause), and integrates levels of organization from the whole animal to the genome, where possible. Several similarities among these states are highlighted, including patterns and regulation of metabolic balance, fuel use, and mitochondrial metabolism. Differences among models are also apparent, particularly in whether the metabolic suppression is intrinsic to the tissue or depends on the whole-animal response. While in these hypometabolic states, tissues from many animals are tolerant of hypoxia/anoxia, ischemia/reperfusion, and disuse. These natural models may, therefore, serve as valuable and instructive models for biomedical research.
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Affiliation(s)
- James F Staples
- Department of Biology, University of Western Ontario, London, Ontario, Canada
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26
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McMillan AC, White MD. Induction of thermogenesis in brown and beige adipose tissues: molecular markers, mild cold exposure and novel therapies. Curr Opin Endocrinol Diabetes Obes 2015; 22:347-52. [PMID: 26313896 DOI: 10.1097/med.0000000000000191] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
PURPOSE OF REVIEW The purpose of this short review paper is to summarize recent developments in the understanding of the activation, growth and function of brown adipose tissue (BAT). RECENT FINDINGS Transcriptional markers for increased BAT activity and differentiation of white adipocytes to 'beige' or 'brite' adipocytes include amongst others peroxisome proliferator-activated receptor γ, cytosine-enhancer-binding protein, positive regulatory domain 16 and bone morphogenetic proteins. These markers induce uncoupling protein 1 expression in brown and 'beige' or 'brite' adipocytes which allows energy from macronutrients to be expended as heat. Acute and repeated mild cold exposures of 17-19 °C in adult humans increase BAT volume and activity and this is a novel method for increasing their energy expenditure. Emerging evidence suggests that irisin and melatonin hormones may be involved in BAT activation. Additionally, brown adipocyte stem cell therapy transplantation is a means to stimulate this increased thermogenesis from brown and 'beige' or 'brite' adipocytes. SUMMARY Markers for increased BAT activation and for white adipocyte differentiation into beige/brite adipocytes have been identified, and these lead to an uncoupling protein 1-mediated increase in metabolic rate. Mild cold exposure and brown adipocyte stem cell transplantation are two potential strategies for inducing activation and growth of BAT for the treatment of human obesity.
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Affiliation(s)
- Andrew C McMillan
- Department of Biomedical Physiology and Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada
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27
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van Breukelen F, Martin SL. The Hibernation Continuum: Physiological and Molecular Aspects of Metabolic Plasticity in Mammals. Physiology (Bethesda) 2015; 30:273-81. [DOI: 10.1152/physiol.00010.2015] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mammals are often considered to be masters of homeostasis, with the ability to maintain a constant internal milieu, despite marked changes in the environment; however, many species exhibit striking physiological and biochemical plasticity in the face of environmental fluctuations. Here, we review metabolic depression and body temperature fluctuation in mammals, with a focus on the extreme example of hibernation in small-bodied eutherian species. Careful exploitation of the phenotypic plasticity of mammals with metabolic flexibility may provide the key to unlocking the molecular secrets of orchestrating and surviving reversible metabolic depression in less plastic species, including humans.
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Affiliation(s)
| | - Sandra L. Martin
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado
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28
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Proteomics approaches shed new light on hibernation physiology. J Comp Physiol B 2015; 185:607-27. [PMID: 25976608 DOI: 10.1007/s00360-015-0905-9] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Revised: 03/11/2015] [Accepted: 04/19/2015] [Indexed: 10/23/2022]
Abstract
The broad phylogenetic distribution and rapid phenotypic transitions of mammalian hibernators imply that hibernation is accomplished by differential expression of common genes. Traditional candidate gene approaches have thus far explained little of the molecular mechanisms underlying hibernation, likely due to (1) incomplete and imprecise sampling of a complex phenotype, and (2) the forming of hypotheses about which genes might be important based on studies of model organisms incapable of such dynamic physiology. Unbiased screening approaches, such as proteomics, offer an alternative means to discover the cellular underpinnings that permit successful hibernation and may reveal previously overlooked, important pathways. Here, we review the findings that have emerged from proteomics studies of hibernation. One striking feature is the stability of the proteome, especially across the extreme physiological shifts of torpor-arousal cycles during hibernation. This has led to subsequent investigations of the role of post-translational protein modifications in altering protein activity without energetically wasteful removal and rebuilding of protein pools. Another unexpected finding is the paucity of universal proteomic adjustments across organ systems in response to the extreme metabolic fluctuations despite the universality of their physiological challenges; rather each organ appears to respond in a unique, tissue-specific manner. Additional research is needed to extend and synthesize these results before it will be possible to address the whole body physiology of hibernation.
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Grabek KR, Diniz Behn C, Barsh GS, Hesselberth JR, Martin SL. Enhanced stability and polyadenylation of select mRNAs support rapid thermogenesis in the brown fat of a hibernator. eLife 2015; 4. [PMID: 25626169 PMCID: PMC4383249 DOI: 10.7554/elife.04517] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Accepted: 12/23/2014] [Indexed: 12/21/2022] Open
Abstract
During hibernation, animals cycle between torpor and arousal. These cycles involve
dramatic but poorly understood mechanisms of dynamic physiological regulation at the
level of gene expression. Each cycle, Brown Adipose Tissue (BAT) drives periodic
arousal from torpor by generating essential heat. We applied digital transcriptome
analysis to precisely timed samples to identify molecular pathways that underlie the
intense activity cycles of hibernator BAT. A cohort of transcripts increased during
torpor, paradoxical because transcription effectively ceases at these low
temperatures. We show that this increase occurs not by elevated transcription but
rather by enhanced stabilization associated with maintenance and/or extension of long
poly(A) tails. Mathematical modeling further supports a temperature-sensitive
mechanism to protect a subset of transcripts from ongoing bulk degradation instead of
increased transcription. This subset was enriched in a C-rich motif and genes
required for BAT activation, suggesting a model and mechanism to prioritize
translation of key proteins for thermogenesis. DOI:http://dx.doi.org/10.7554/eLife.04517.001 Many mammals hibernate to avoid food scarcity and harsh conditions during winter.
Hibernation involves entering a state called torpor, which drastically reduces the
amount of energy used by the body. During torpor, body temperature also decreases.
This is particularly exemplified in ground squirrels, whose body temperature can
hover at just above or even below the point of freezing. However, hibernating mammals
cannot remain in this state continuously over the months of hibernation but instead
cycle between bouts of torpor lasting for 1–3 weeks and brief periods of
‘arousal’ lasting between 12–24 hr, during which their body
rapidly warms up. The heat required to start warming up the hibernator is generated from a specialized
form of fat called brown adipose tissue. Normally, the bursts of metabolic activity
that are required to create this heat depend on certain proteins being produced.
Making a protein involves ‘translating’ its sequence from template
molecules called messenger RNA (mRNA), which are ‘transcribed’ from the
gene that encodes the protein. During the low body temperatures experienced during
torpor, both of these processes stop. So how is the hibernator able to quickly and
efficiently heat itself up during the arousal periods of hibernation? Grabek et al. investigated this by analyzing the relative levels of mRNA in the brown
adipose tissue of hibernating 13-lined ground squirrels. Using a special technique to
sample and sequence small fragments of mRNA taken from brown adipose tissue, Grabek
et al. compiled a profile of the mRNA molecules present at different points in the
torpor–arousal cycle and compared this with a similar profile taken from
squirrels that were not hibernating. From this analysis, Grabek et al. detected that a particular group of mRNA molecules
that are required for producing heat increase in abundance during torpor, even though
body temperature is low enough to stop gene transcription. This increased abundance
does not occur because more of the mRNA molecules are made; instead, the mRNA
molecules are modified to become more stable and long lasting. Once the animal warms
up during arousal, gene transcription is reactivated and more new mRNA molecules are
made. Grabek et al. suggest that the key mRNAs required for brown adipose tissue function
are selectively stabilized during torpor through a temperature-dependent protective
mechanism. These mRNAs are then preferentially translated into proteins during
arousal to rapidly and efficiently heat the hibernator. Most other mRNA molecules
degrade throughout torpor, and so their numbers decline as replacements are not
transcribed until body temperature briefly recovers during arousal. Whether this
protective mechanism is also used in other tissues during torpor remains a question
for future work. DOI:http://dx.doi.org/10.7554/eLife.04517.002
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Affiliation(s)
- Katharine R Grabek
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, United States
| | - Cecilia Diniz Behn
- Department of Applied Math and Statistics, Colorado School of Mines, Golden, United States
| | - Gregory S Barsh
- Department of Research, HudsonAlpha Institute for Biotechnology, Huntsville, United States
| | - Jay R Hesselberth
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, United States
| | - Sandra L Martin
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, United States
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Hindle AG, Otis JP, Epperson LE, Hornberger TA, Goodman CA, Carey HV, Martin SL. Prioritization of skeletal muscle growth for emergence from hibernation. ACTA ACUST UNITED AC 2014; 218:276-84. [PMID: 25452506 DOI: 10.1242/jeb.109512] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Mammalian hibernators provide an extreme example of naturally occurring challenges to muscle homeostasis. The annual hibernation cycle is characterized by shifts between summer euthermy with tissue anabolism and accumulation of body fat reserves, and winter heterothermy with fasting and tissue catabolism. The circannual patterns of skeletal muscle remodelling must accommodate extended inactivity during winter torpor, the motor requirements of transient winter active periods, and sustained activity following spring emergence. Muscle volume in thirteen-lined ground squirrels (Ictidomys tridecemlineatus) calculated from MRI upper hindlimb images (n=6 squirrels, n=10 serial scans) declined from hibernation onset, reaching a nadir in early February. Paradoxically, mean muscle volume rose sharply after February despite ongoing hibernation, and continued total body mass decline until April. Correspondingly, the ratio of muscle volume to body mass was steady during winter atrophy (October-February) but increased (+70%) from February to May, which significantly outpaced changes in liver or kidney examined by the same method. Generally stable myocyte cross-sectional area and density indicated that muscle remodelling is well regulated in this hibernator, despite vastly altered seasonal fuel and activity levels. Body composition analysis by echo MRI showed lean tissue preservation throughout hibernation amid declining fat mass by the end of winter. Muscle protein synthesis was 66% depressed in early but not late winter compared with a summer fasted baseline, while no significant changes were observed in the heart, liver or intestine, providing evidence that could support a transition in skeletal muscle regulation between early and late winter, prior to spring emergence and re-feeding.
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Affiliation(s)
- Allyson G Hindle
- Cell & Developmental Biology, University of Colorado School of Medicine, Mail Stop 8108, 12801 East 17th Avenue, Aurora, CO 80045, USA
| | - Jessica P Otis
- Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
| | - L Elaine Epperson
- Cell & Developmental Biology, University of Colorado School of Medicine, Mail Stop 8108, 12801 East 17th Avenue, Aurora, CO 80045, USA
| | - Troy A Hornberger
- Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
| | - Craig A Goodman
- Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
| | - Hannah V Carey
- Comparative Biosciences, School of Veterinary Medicine, University of Wisconsin, Madison, WI 53706, USA
| | - Sandra L Martin
- Cell & Developmental Biology, University of Colorado School of Medicine, Mail Stop 8108, 12801 East 17th Avenue, Aurora, CO 80045, USA
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Abstract
As part of a current worldwide effort to understand the physiology of human BAT (hBAT) and whether its thermogenic activity can be manipulated to treat obesity, the workshop "Exploring the Roles of Brown Fat in Humans" was convened at the National Institutes of Health on February 25-26, 2014. Presentations and discussion indicated that hBAT and its physiological roles are highly complex, and research is needed to understand the health impact of hBAT beyond thermogenesis and body weight regulation, and to define its interactions with core physiological processes like glucose homeostasis, cachexia, physical activity, bone structure, sleep, and circadian rhythms.
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Affiliation(s)
- Aaron M Cypess
- Research Division, Joslin Diabetes Center, Harvard Medical School, Boston, MA 02215, USA
| | - Carol R Haft
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Maren R Laughlin
- National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
| | - Houchun H Hu
- Department of Radiology, Children's Hospital Los Angeles, Los Angeles, CA 90027, USA
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Martin SL. Intrinsic circannual rhythm controls protein dynamics in a hibernator to support rapid heat production. Temperature (Austin) 2014; 1:80-1. [PMID: 27581746 PMCID: PMC4977172 DOI: 10.4161/temp.29627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2014] [Revised: 06/16/2014] [Accepted: 06/17/2014] [Indexed: 11/21/2022] Open
Abstract
A proteomics screen of brown adipose tissue in 13-lined ground squirrels reveals protein changes underlying the extreme recruitment and activity cycles characteristic of this organ in small eutherian hibernators. Protein changes precede changes in physiology, indicating endogenous timing rather than ambient temperature controls the annual recruitment-atrophy cycle in this obligate hibernator.
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Affiliation(s)
- Sandra L Martin
- Department of Cell and Developmental Biology; University of Colorado School of Medicine; Aurora, CO USA
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Hindle AG, Grabek KR, Epperson LE, Karimpour-Fard A, Martin SL. Metabolic changes associated with the long winter fast dominate the liver proteome in 13-lined ground squirrels. Physiol Genomics 2014; 46:348-61. [PMID: 24642758 DOI: 10.1152/physiolgenomics.00190.2013] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Small-bodied hibernators partition the year between active homeothermy and hibernating heterothermy accompanied by fasting. To define molecular events underlying hibernation that are both dependent and independent of fasting, we analyzed the liver proteome among two active and four hibernation states in 13-lined ground squirrels. We also examined fall animals transitioning between fed homeothermy and fasting heterothermy. Significantly enriched pathways differing between activity and hibernation were biased toward metabolic enzymes, concordant with the fuel shifts accompanying fasting physiology. Although metabolic reprogramming to support fasting dominated these data, arousing (rewarming) animals had the most distinct proteome among the hibernation states. Instead of a dominant metabolic enzyme signature, torpor-arousal cycles featured differences in plasma proteins and intracellular membrane traffic and its regulation. Phosphorylated NSFL1C, a membrane regulator, exhibited this torpor-arousal cycle pattern; its role in autophagosome formation may promote utilization of local substrates upon metabolic reactivation in arousal. Fall animals transitioning to hibernation lagged in their proteomic adjustment, indicating that the liver is more responsive than preparatory to the metabolic reprogramming of hibernation. Specifically, torpor use had little impact on the fall liver proteome, consistent with a dominant role of nutritional status. In contrast to our prediction of reprogramming the transition between activity and hibernation by gene expression and then within-hibernation transitions by posttranslational modification (PTM), we found extremely limited evidence of reversible PTMs within torpor-arousal cycles. Rather, acetylation contributed to seasonal differences, being highest in winter (specifically in torpor), consistent with fasting physiology and decreased abundance of the mitochondrial deacetylase, SIRT3.
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Affiliation(s)
- Allyson G Hindle
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado
| | - Katharine R Grabek
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado; Human Medical Genetics and Genomics Program, University of Colorado School of Medicine, Aurora, Colorado; and
| | - L Elaine Epperson
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado
| | - Anis Karimpour-Fard
- Center for Computational Pharmacology University of Colorado School of Medicine, Aurora, Colorado
| | - Sandra L Martin
- Department of Cell and Developmental Biology, University of Colorado School of Medicine, Aurora, Colorado; Human Medical Genetics and Genomics Program, University of Colorado School of Medicine, Aurora, Colorado; and
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