1
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Wade S, Hadj-Moussa H, Storey KB. mRNA m 6 A methylation in wood frog brain is maintained during freezing and anoxia. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART A, ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY 2023; 339:325-334. [PMID: 36703486 DOI: 10.1002/jez.2681] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2022] [Revised: 01/08/2023] [Accepted: 01/10/2023] [Indexed: 01/28/2023]
Abstract
Freeze tolerance is an adaptive strategy that wood frogs (Rana sylvatica) use to survive the subzero temperatures of winter. It is characterized by a variety of metabolic and physiological changes that facilitate successful freezing and anoxia. As both mRNA regulation and posttranslation protein modification have been implicated in freeze tolerance, we hypothesized that posttranslational RNA regulation is also involved in coordinating freeze-thaw cycles and metabolic rate depression. As such, we investigated the most abundant RNA modification, adenosine methylation (N6 -methyladenosine; m6 A) in wood frog brains during 24 h periods of freezing and anoxia. This was followed by an examination of levels of RNA methyltransferases, demethyltransferases, and the readers of RNA methylation. Despite relative levels of methylation on mRNA remaining constant throughout freezing and anoxia, a significant increase in relative abundance of m6 A methyltransferases METTL3 and METTL14 was observed. In addition, we investigated the effect of m6 A RNA methylation on mRNA triaging to stress granules and report a significant increase in stress granule markers TIAR and TIA-1 in both freezing and anoxia. Our findings are the first report of RNA posttranslational regulation during metabolic rate depression in the wood frog brain and suggest that the dynamic RNA methylation observed is not directly linked to mRNA regulation during periods of extreme metabolic reorganization, warranting future investigations.
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Affiliation(s)
- Steven Wade
- Department of Biology, Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada.,Department of Biochemistry, Immunology and Microbiology, Faculty of Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Hanane Hadj-Moussa
- Department of Biology, Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada.,Epigenetics Programme, Babraham Institute, Cambridge, UK
| | - Kenneth B Storey
- Department of Biology, Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada
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2
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Velasco BR, Izquierdo JM. T-Cell Intracellular Antigen 1-Like Protein in Physiology and Pathology. Int J Mol Sci 2022; 23:ijms23147836. [PMID: 35887183 PMCID: PMC9318959 DOI: 10.3390/ijms23147836] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 07/13/2022] [Accepted: 07/14/2022] [Indexed: 11/16/2022] Open
Abstract
T-cell intracellular antigen 1 (TIA1)-related/like (TIAR/TIAL1) protein is a multifunctional RNA-binding protein (RBP) involved in regulating many aspects of gene expression, independently or in combination with its paralog TIA1. TIAR was first described in 1992 by Paul Anderson’s lab in relation to the development of a cell death phenotype in immune system cells, as it possesses nucleolytic activity against cytotoxic lymphocyte target cells. Similar to TIA1, it is characterized by a subcellular nucleo-cytoplasmic localization and ubiquitous expression in the cells of different tissues of higher organisms. In this paper, we review the relevant structural and functional information available about TIAR from a triple perspective (molecular, cellular and pathophysiological), paying special attention to its expression and regulation in cellular events and processes linked to human pathophysiology.
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3
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Tessier SN, Ingelson-Filpula WA, Storey KB. Epigenetic regulation by DNA methyltransferases during torpor in the thirteen-lined ground squirrel Ictidomys tridecemlineatus. Mol Cell Biochem 2021; 476:3975-3985. [PMID: 34191233 DOI: 10.1007/s11010-021-04214-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Accepted: 06/21/2021] [Indexed: 12/31/2022]
Abstract
The thirteen-lined ground squirrel, Ictidomys tridecemlineatus, is a mammal capable of lowering its Tb to almost 0 °C while undergoing deep torpor bouts over the winter. To decrease its metabolic rate to such a drastic extent, the squirrel must undergo multiple physiological, biological, and molecular alterations including downregulation of almost all nonessential processes. Epigenetic regulation allows for a dynamic range of transient phenotypes, allowing the squirrel to downregulate energy-expensive and nonessential pathways during torpor. DNA methylation is a prominent form of epigenetic regulation; therefore, the DNA methyltransferase (DNMT) family of enzymes were studied by measuring expression and activity levels of the five major proteins during torpor bouts. Additionally, specific cytosine marks on genomic DNA were quantified to further elucidate DNA methylation during hibernation. A tissue-specific response was observed that highlighted variant degrees of DNA methylation and DNMT expression/activity, demonstrating that DNA methylation is a highly complex form of epigenetic regulation and likely one of many regulatory mechanisms that enables metabolic rate depression in response to torpor.
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Affiliation(s)
- Shannon N Tessier
- Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.,BioMEMS Resource Center & Center for Engineering in Medicine, Massachusetts General Hospital & Harvard Medical School, 114 16th Street, Charlestown, MA, 02129, USA
| | - W Aline Ingelson-Filpula
- Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada
| | - Kenneth B Storey
- Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.
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4
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Logan SM, Storey KB. Cold-inducible RNA-binding protein Cirp, but not Rbm3, may regulate transcript processing and protection in tissues of the hibernating ground squirrel. Cell Stress Chaperones 2020; 25:857-868. [PMID: 32307648 PMCID: PMC7591650 DOI: 10.1007/s12192-020-01110-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Revised: 03/31/2020] [Accepted: 04/02/2020] [Indexed: 12/31/2022] Open
Abstract
RNA-binding proteins (RBPs) have important roles in transcription, pre-mRNA processing/transport, mRNA degradation, translation, and non-coding RNA processing, among others. RBPs that are expressed in response to cold stress, such as Cirp and Rbm3, could regulate RNA stability and translation in hibernating mammals that reduce their body temperatures from 37 °C to as low as 0-5 °C during torpor bouts. RBPs including Cirp, Rbm3, and stress-inducible HuR translocate from the nucleus to stabilize mRNAs in the cytoplasm, and thereby could regulate which mRNA transcripts are protected from degradation and are translated, versus stored, for future protein synthesis or degraded by nucleases during cell stress associated with metabolic rate depression. This is the first study to explore the transcriptional/translational regulation, and subcellular localization of cold-inducible RBPs in a model hibernator, the 13-lined ground squirrel (Ictidomys tridecemlineatus). Cirp protein levels were upregulated in liver, skeletal muscle, and brown adipose tissue throughout the torpor-arousal cycle whereas Rbm3 protein levels stayed constant or decreased, suggesting an important role for Cirp, but likely not Rbm3, in the hibernator stress response. Increased cytoplasmic localization of Cirp in liver and muscle and HuR in liver during torpor, but no changes in the relative levels of Rbm3 in the cytoplasm, emphasizes a role for Cirp and possibly HuR in regulating mRNA processing during torpor. This study informs our understanding of the natural adaptations that extreme animals use in the face of stress, and highlight natural stress response mediators that could be used to bolster cryoprotection of human organs donated for transplant.
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Affiliation(s)
- Samantha M Logan
- Departments of Biology and Chemistry, Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada
| | - Kenneth B Storey
- Departments of Biology and Chemistry, Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada.
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5
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Luu BE, Lefai E, Giroud S, Swenson JE, Chazarin B, Gauquelin-Koch G, Arnemo JM, Evans AL, Bertile F, Storey KB. MicroRNAs facilitate skeletal muscle maintenance and metabolic suppression in hibernating brown bears. J Cell Physiol 2020; 235:3984-3993. [PMID: 31643088 DOI: 10.1002/jcp.29294] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2019] [Accepted: 09/30/2019] [Indexed: 02/06/2023]
Abstract
Hibernating brown bears, Ursus arctos, undergo extended periods of inactivity and yet these large hibernators are resilient to muscle disuse atrophy. Physiological characteristics associated with atrophy resistance in bear muscle have been examined (e.g., muscle mechanics, neural activity) but roles for molecular signaling/regulatory mechanisms in the resistance to muscle wasting in bears still require investigation. Using quantitative reverse transcription PCR (RT-qPCR), the present study characterized the responses of 36 microRNAs linked with development, metabolism, and regeneration of skeletal muscle, in the vastus lateralis of brown bears comparing winter hibernating and summer active animals. Relative levels of mRNA of selected genes (mef2a, pax7, id2, prkaa1, and mstn) implicated upstream and downstream of the microRNAs were examined. Results indicated that hibernation elicited a myogenic microRNA, or "myomiR", response via MEF2A-mediated signaling. Upregulation of MEF2A-controlled miR-1 and miR-206 and respective downregulation of pax7 and id2 mRNA are suggestive of responses that promote skeletal muscle maintenance. Increased levels of metabolic microRNAs, such as miR-27, miR-29, and miR-33, may facilitate metabolic suppression during hibernation via mechanisms that decrease glucose uptake and fatty acid oxidation. This study identified myomiR-mediated mechanisms for the promotion of muscle regeneration, suppression of ubiquitin ligases, and resistance to muscle atrophy during hibernation mediated by observed increases in miR-206, miR-221, miR-31, miR-23a, and miR-29b. This was further supported by the downregulation of myomiRs associated with a muscle injury and inflammation (miR-199a and miR-223) during hibernation. The present study provides evidence of myomiR-mediated signaling pathways that are activated during hibernation to maintain skeletal muscle functionality in brown bears.
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Affiliation(s)
- Bryan E Luu
- Department of Biology, Carleton University, Ottawa, Canada
- Faculty of Medicine, McGill University, Montréal, Québec, Canada
| | - Etienne Lefai
- Université d'Auvergne, INRA, Unité de Nutrition Humaine, Clermont-Ferrand, France
| | - Sylvain Giroud
- Research Institute of Wildlife Ecology, Department of Interdisciplinary Life Sciences, University of Veterinary Medicine, Vienna, Austria
| | - Jon E Swenson
- Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, Ås, Norway
- Norwegian Institute for Nature Research, Trondheim, Norway
| | - Blandine Chazarin
- Centre National d'Etudes Spatiales, CNES, Paris, France
- Université de Strasbourg, CNRS, IPHC, Strasbourg, France
| | | | - Jon M Arnemo
- Department of Forestry and Wildlife Management, Inland Norway University of Applied Sciences, Koppang, Norway
- Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden
| | - Alina L Evans
- Department of Forestry and Wildlife Management, Inland Norway University of Applied Sciences, Koppang, Norway
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6
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Biggar KK, Storey KB. Functional impact of microRNA regulation in models of extreme stress adaptation. J Mol Cell Biol 2019; 10:93-101. [PMID: 29206937 DOI: 10.1093/jmcb/mjx053] [Citation(s) in RCA: 55] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2017] [Accepted: 11/30/2017] [Indexed: 01/12/2023] Open
Abstract
When confronted with severe environmental stress, some animals are able to undergo a substantial reorganization of their cellular environment that enables long-term survival. One molecular mechanism of adaptation that has received considerable attention in recent years has been the action of reversible transcriptome regulation by microRNA. The implementation of new computational and high-throughput experimental approaches has started to uncover the vital contributions of microRNA towards stress adaptation. Indeed, recent studies have suggested that microRNA may have a major regulatory influence over a number of cellular processes that are essential to prolonged environmental stress survival. To date, a number of studies have highlighted the role of microRNA in the regulation of a metabolically depressed state, documenting stress-responsive microRNA expression during mammalian hibernation, frog and insect freeze tolerance, and turtle and marine snail anoxia tolerance. These studies collectively indicate a conserved principle of microRNA stress response across phylogeny. As we are on the verge of dissecting the role of microRNA in environmental stress adaptation, this review summarizes recent research advances and the hallmark expression patterns that facilitate stress survival.
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Affiliation(s)
- Kyle K Biggar
- Institute of Biochemistry & Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada
| | - Kenneth B Storey
- Institute of Biochemistry & Department of Biology, Carleton University, Ottawa, ON K1S 5B6, Canada
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7
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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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8
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Wu CW, Biggar KK, Luu BE, Szereszewski KE, Storey KB. Analysis of microRNA expression during the torpor-arousal cycle of a mammalian hibernator, the 13-lined ground squirrel. Physiol Genomics 2016; 48:388-96. [PMID: 27084747 DOI: 10.1152/physiolgenomics.00005.2016] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 04/04/2016] [Indexed: 01/06/2023] Open
Abstract
Hibernation is a highly regulated stress response that is utilized by some mammals to survive harsh winter conditions and involves a complex metabolic reprogramming at the cellular level to maintain tissue protections at low temperature. In this study, we profiled the expression of 117 conserved microRNAs in the heart, muscle, and liver of the 13-lined ground squirrel (Ictidomys tridecemlineatus) across four stages of the torpor-arousal cycle (euthermia, early torpor, late torpor, and interbout arousal) by real-time PCR. We found significant differential regulation of numerous microRNAs that were both tissue specific and torpor stage specific. Among the most significant regulated microRNAs was miR-208b, a positive regulator of muscle development that was found to be upregulated by fivefold in the heart during late torpor (13-fold during arousal), while decreased by 3.7-fold in the skeletal muscle, implicating a potential regulatory role in the development of cardiac hypertrophy and skeletal muscle atrophy in the ground squirrels during torpor. In addition, the insulin resistance marker miR-181a was upregulated by 5.7-fold in the liver during early torpor, which supports previous suggestions of hyperinsulinemia in hibernators during the early stages of the hibernation cycle. Although microRNA expression profiles were largely unique between the three tissues, GO annotation analysis revealed that the putative targets of upregulated microRNAs tend to enrich toward suppression of progrowth-related processes in all three tissues. These findings implicate microRNAs in the regulation of both tissue-specific processes and general suppression of cell growth during hibernation.
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Affiliation(s)
- Cheng-Wei Wu
- Institute of Biochemistry and Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Kyle K Biggar
- Institute of Biochemistry and Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Bryan E Luu
- Institute of Biochemistry and Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Kama E Szereszewski
- Institute of Biochemistry and Department of Biology, Carleton University, Ottawa, Ontario, Canada
| | - Kenneth B Storey
- Institute of Biochemistry and Department of Biology, Carleton University, Ottawa, Ontario, Canada
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9
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Alvarado S, Mak T, Liu S, Storey KB, Szyf M. Dynamic changes in global and gene-specific DNA methylation during hibernation in adult thirteen-lined ground squirrels, Ictidomys tridecemlineatus. ACTA ACUST UNITED AC 2015; 218:1787-95. [PMID: 25908059 DOI: 10.1242/jeb.116046] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Accepted: 04/15/2015] [Indexed: 12/21/2022]
Abstract
Hibernating mammals conserve energy in the winter by undergoing prolonged bouts of torpor, interspersed with brief arousals back to euthermia. These bouts are accompanied by a suite of reversible physiological and biochemical changes; however, much remains to be discovered about the molecular mechanisms involved. Given the seasonal nature of hibernation, it stands to reason that underlying plastic epigenetic mechanisms should exist. One such form of epigenomic regulation involves the reversible modification of cytosine bases in DNA by methylation. DNA methylation is well known to be a mechanism that confers upon DNA its cellular identity during differentiation in response to innate developmental cues. However, it has recently been hypothesized that DNA methylation also acts as a mechanism for adapting genome function to changing external environmental and experiential signals over different time scales, including during adulthood. Here, we tested the hypothesis that DNA methylation is altered during hibernation in adult wild animals. This study evaluated global changes in DNA methylation in response to hibernation in the liver and skeletal muscle of thirteen-lined ground squirrels along with changes in expression of DNA methyltransferases (DNMT1/3B) and methyl binding domain proteins (MBDs). A reduction in global DNA methylation occurred in muscle during torpor phases whereas significant changes in DNMTs and MBDs were seen in both tissues. We also report dynamic changes in DNA methylation in the promoter of the myocyte enhancer factor 2C (mef2c) gene, a candidate regulator of metabolism in skeletal muscle. Taken together, these data show that genomic DNA methylation is dynamic across torpor-arousal bouts during winter hibernation, consistent with a role for this regulatory mechanism in contributing to the hibernation phenotype.
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Affiliation(s)
- Sebastian Alvarado
- Department of Pharmacology, McGill University, 3655 Sir William Osler Suite 1309, Montreal, QC, Canada H3G 1Y6; Sackler program in Epigenetics and Psychobiology at McGill University
| | - Timothy Mak
- Department of Pharmacology, McGill University, 3655 Sir William Osler Suite 1309, Montreal, QC, Canada H3G 1Y6; Sackler program in Epigenetics and Psychobiology at McGill University
| | - Sara Liu
- Department of Pharmacology, McGill University, 3655 Sir William Osler Suite 1309, Montreal, QC, Canada H3G 1Y6; Sackler program in Epigenetics and Psychobiology at McGill University
| | - Kenneth B Storey
- Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K1S 5B6
| | - Moshe Szyf
- Department of Pharmacology, McGill University, 3655 Sir William Osler Suite 1309, Montreal, QC, Canada H3G 1Y6; Sackler program in Epigenetics and Psychobiology at McGill University
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10
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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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11
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Abstract
For many animals, survival of severe environmental stress (e.g. to extremes of heat or cold, drought, oxygen limitation, food deprivation) is aided by entry into a hypometabolic state. Strong depression of metabolic rate, often to only 1–20% of normal resting rate, is a core survival strategy of multiple forms of hypometabolism across the animal kingdom, including hibernation, anaerobiosis, aestivation and freeze tolerance. Global biochemical controls are needed to suppress and reprioritize energy use; one such well-studied control is reversible protein phosphorylation. Recently, we turned our attention to the idea that mechanisms previously associated mainly with epigenetic regulation can also contribute to reversible suppression of gene expression in hypometabolic states. Indeed, situations as diverse as mammalian hibernation and turtle anoxia tolerance show coordinated changes in histone post-translational modifications (acetylation, phosphorylation) and activities of histone deacetylases, consistent with their use as mechanisms for suppressing gene expression during hypometabolism. Other potential mechanisms of gene silencing in hypometabolic states include altered expression of miRNAs that can provide post-transcriptional suppression of mRNA translation and the formation of ribonuclear protein bodies in the nucleus and cytoplasm to allow storage of mRNA transcripts until animals rouse themselves again. Furthermore, mechanisms first identified in epigenetic regulation (e.g. protein acetylation) are now proving to apply to many central metabolic enzymes (e.g. lactate dehydrogenase), suggesting a new layer of regulatory control that can contribute to coordinating the depression of metabolic rate.
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Affiliation(s)
- Kenneth B. Storey
- Institute of Biochemistry and Departments of Biology and Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada
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12
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Tessier SN, Storey KB. To be or not to be: the regulation of mRNA fate as a survival strategy during mammalian hibernation. Cell Stress Chaperones 2014; 19:763-76. [PMID: 24789358 PMCID: PMC4389848 DOI: 10.1007/s12192-014-0512-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 04/13/2014] [Indexed: 12/20/2022] Open
Abstract
Mammalian hibernators undergo profound behavioral, physiological, and biochemical changes in order to cope with hypothermia, ischemia-reperfusion, and finite fuel reserves over days or weeks of continuous torpor. Against a backdrop of global reductions in energy-expensive processes such as transcription and translation, a subset of genes/proteins are strategically upregulated in order to meet challenges associated with hibernation. Consequently, hibernation involves substantial transcriptional and posttranscriptional regulatory mechanisms and provides a phenomenon with which to understand how a set of common genes/proteins can be differentially regulated in order to enhance stress tolerance beyond that which is possible for nonhibernators. The present review focuses on the involvement of messenger RNA (mRNA) interacting factors that play a role in the regulation of gene/protein expression programs that define the hibernating phenotype. These include proteins involved in mRNA processing (i.e., capping, splicing, and polyadenylation) and the possible role of alternative splicing as a means of enhancing protein diversity. Since the total pool of mRNA remains constant throughout torpor, mechanisms which enhance mRNA stability are discussed in the context of RNA binding proteins and mRNA decay pathways. Furthermore, mechanisms which control the global reduction of cap-dependent translation and the involvement of internal ribosome entry sites in mRNAs encoding stress response proteins are also discussed. Finally, the concept of regulating each of these factors in discrete subcellular compartments for enhanced efficiency is addressed. The analysis draws on recent research from several well-studied mammalian hibernators including ground squirrels, bats, and bears.
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Affiliation(s)
- Shannon N. Tessier
- Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6 Canada
| | - Kenneth B. Storey
- Institute of Biochemistry & Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6 Canada
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