1
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Hu M, Santin JM. Transformation to ischaemia tolerance of frog brain function corresponds to dynamic changes in mRNA co-expression across metabolic pathways. Proc Biol Sci 2022; 289:20221131. [PMID: 35892220 PMCID: PMC9326273 DOI: 10.1098/rspb.2022.1131] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Neural activity is costly and requires continuous ATP from aerobic metabolism. Brainstem motor function of American bullfrogs normally collapses after minutes of ischaemia, but following hibernation, it becomes ischaemia-tolerant, generating output for up to 2 h without oxygen or glucose delivery. Transforming the brainstem to function during ischaemia involves a switch to anaerobic glycolysis and brain glycogen. We hypothesized that improving neural performance during ischaemia involves a transcriptional program for glycogen and glucose metabolism. Here we measured mRNA copy number of genes along the path from glycogen metabolism to lactate production using real-time quantitative PCR. The expression of individual genes did not reflect enhanced glucose metabolism. However, the number of co-expressed gene pairs increased early into hibernation, and by the end, most genes involved in glycogen metabolism, glucose transport and glycolysis exhibited striking linear co-expression. By contrast, co-expression of genes in the Krebs cycle and electron transport chain decreased throughout hibernation. Our results uncover reorganization of the metabolic transcriptional network associated with a shift to ischaemia tolerance in brain function. We conclude that modifying gene co-expression may be a critical step in synchronizing storage and use of glucose to achieve ischaemia tolerance in active neural circuits.
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Affiliation(s)
- Min Hu
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, USA
| | - Joseph M. Santin
- Department of Biology, University of North Carolina at Greensboro, Greensboro, NC, USA
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2
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Myrka A, Buck L. Cytoskeletal Arrest: An Anoxia Tolerance Mechanism. Metabolites 2021; 11:metabo11080561. [PMID: 34436502 PMCID: PMC8401981 DOI: 10.3390/metabo11080561] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 08/13/2021] [Accepted: 08/14/2021] [Indexed: 12/16/2022] Open
Abstract
Polymerization of actin filaments and microtubules constitutes a ubiquitous demand for cellular adenosine-5′-triphosphate (ATP) and guanosine-5′-triphosphate (GTP). In anoxia-tolerant animals, ATP consumption is minimized during overwintering conditions, but little is known about the role of cell structure in anoxia tolerance. Studies of overwintering mammals have revealed that microtubule stability in neurites is reduced at low temperature, resulting in withdrawal of neurites and reduced abundance of excitatory synapses. Literature for turtles is consistent with a similar downregulation of peripheral cytoskeletal activity in brain and liver during anoxic overwintering. Downregulation of actin dynamics, as well as modification to microtubule organization, may play vital roles in facilitating anoxia tolerance. Mitochondrial calcium release occurs during anoxia in turtle neurons, and subsequent activation of calcium-binding proteins likely regulates cytoskeletal stability. Production of reactive oxygen species (ROS) formation can lead to catastrophic cytoskeletal damage during overwintering and ROS production can be regulated by the dynamics of mitochondrial interconnectivity. Therefore, suppression of ROS formation is likely an important aspect of cytoskeletal arrest. Furthermore, gasotransmitters can regulate ROS levels, as well as cytoskeletal contractility and rearrangement. In this review we will explore the energetic costs of cytoskeletal activity, the cellular mechanisms regulating it, and the potential for cytoskeletal arrest being an important mechanism permitting long-term anoxia survival in anoxia-tolerant species, such as the western painted turtle and goldfish.
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Affiliation(s)
- Alexander Myrka
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada;
| | - Leslie Buck
- Department of Cell and Systems Biology, University of Toronto, Toronto, ON M5S 3G5, Canada;
- Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON M5S 3G5, Canada
- Correspondence: ; Tel.: +1-416-978-3506
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3
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Wijenayake S, Storey KB. Oxidative Damage? Not a Problem! The Characterization of Humanin-like Mitochondrial Peptide in Anoxia Tolerant Freshwater Turtles. Protein J 2021; 40:87-107. [PMID: 33387248 DOI: 10.1007/s10930-020-09944-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/25/2020] [Indexed: 11/30/2022]
Abstract
Mitochondria was long thought to be an "end function" organelle that regulated the metabolic flux and apoptosis in the cell. However, with the discovery of the mitochondrial peptide (MDP) humanin (HN/MTRNR2), the cytoprotective and pro-survival applications of MDPs have taken the forefront of therapeutic and diagnostic research. However, the regulation of humanin-like MDPs in natural model systems that can tolerate lethal environmental and cytotoxic insults remains to be investigated. Red-eared sliders are champion anaerobes that can withstand three continuous months of anoxia followed by rapid bouts of oxygen reperfusion without incurring cellular damage. Freshwater turtles employ extensive physiological and biochemical strategies to combat anoxia, with metabolic rate depression and a global enhancement of antioxidant and cytoprotective pathways being the two most important contributors. The main aim of this study was to uncover and characterize the humanin-homologue in freshwater turtles as well as investigate the differential regulation of humanin in response to short and long-term oxygen deprivation. In this study we have used de novo and homology-based protein modelling to elucidate the putative structure of humanin in red-eared sliders as well as an ELISA and western immunoblotting to confirm the protein abundance in the turtle brain and six peripheral tissues during control, 5 h, and 20 h anoxia (n = 4/group). We found that a humanin-homologue (TSE-humanin) is present in red-eared sliders and it may play a cytoprotective role against oxidative damage.
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Affiliation(s)
- Sanoji Wijenayake
- Department of Biology, Institute of Biochemistry, Carleton University, Ottawa, ON, Canada.,Department of Biological Sciences and Center for Environmental Epigenetics and Development, University of Toronto, Toronto, ON, Canada
| | - Kenneth B Storey
- Department of Biology, Institute of Biochemistry, Carleton University, Ottawa, ON, Canada. .,Department of Chemistry, Institute of Biochemistry, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.
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4
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Dynamic regulation of histone H3 lysine (K) acetylation and deacetylation during prolonged oxygen deprivation in a champion anaerobe. Mol Cell Biochem 2020; 474:229-241. [PMID: 32729004 DOI: 10.1007/s11010-020-03848-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 07/20/2020] [Indexed: 12/14/2022]
Abstract
Trachemys scripta elegans can survive up to three months of absolute anoxia at 3 °C and recover with minimal cellular damage. Red-eared sliders employ various physiological and biochemical adaptations to survive anoxia with metabolic rate depression (MRD) being the most prominent adaptation. MRD is mediated by epigenetic, transcriptional, post-transcriptional, and post-translational mechanisms aimed at shutting down cellular processes that are not needed for anoxia survival, while reprioritizing ATP towards cell processes that are vital for anaerobiosis. Histone acetylation/deacetylation are epigenetic modifications that maintain a proper balance between permissive chromatin and restricted chromatin, yet very little is known about protein regulation and enzymatic activity of the writers and erasers of acetylation during natural anoxia tolerance. As such, this study explored the interplay between transcriptional activators, histone acetyltransferases (HATs), and transcriptional repressors, sirtuins (SIRTs), along with three prominent acetyl-lysine (K) moieties of histone H3 in the liver of red-eared sliders. Western immunoblotting was used to measure acetylation levels of H3-K14, H3-K18, and H3-K56, as well as protein levels of histone H3-total, HATs, and nuclear SIRTs in the liver in response to 5 h and 20 h anoxia. Global and nuclear enzymatic activity of HATs and enzymatic activity of nuclear SIRTs were also measured. Overall, a strong suppression of HATs-mediated H3 acetylation and SIRT-mediated deacetylation was evident in the liver of red-eared sliders that could play an important role in ATP conservation as part of the overall reduction in metabolic rate.
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5
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Cox GK, Gillis TE. Surviving anoxia: the maintenance of energy production and tissue integrity during anoxia and reoxygenation. J Exp Biol 2020; 223:223/13/jeb207613. [DOI: 10.1242/jeb.207613] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
ABSTRACT
The development of anoxia within tissues represents a significant challenge to most animals because of the decreased capacity for aerobic ATP production, the associated loss of essential cellular functions and the potential for detrimental tissue oxidation upon reoxygenation. Despite these challenges, there are many animals from multiple phyla that routinely experience anoxia and can fully recover. In this Review, we integrate knowledge gained from studies of anoxia-tolerant species across many animal taxa. We primarily focus on strategies used to reduce energy requirements, minimize the consequences of anaerobic ATP production and reduce the adverse effects of reactive oxygen species, which are responsible for tissue damage with reoxygenation. We aim to identify common strategies, as well as novel solutions, to the challenges of anoxia exposure. This Review chronologically examines the challenges faced by animals as they enter anoxia, as they attempt to maintain physiological function during prolonged anoxic exposure and, finally, as they emerge from anoxia. The capacity of animals to survive anoxia is also considered in relation to the increasing prevalence of anoxic zones within marine and freshwater environments, and the need to understand what limits survival.
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Affiliation(s)
- Georgina K. Cox
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
| | - Todd E. Gillis
- Department of Integrative Biology, University of Guelph, Guelph, ON, Canada, N1G 2W1
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6
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Cheung JY, Merali S, Wang J, Zhang XQ, Song J, Merali C, Tomar D, You H, Judenherc-Haouzi A, Haouzi P. The central role of protein kinase C epsilon in cyanide cardiotoxicity and its treatment. Toxicol Sci 2019; 171:247-257. [PMID: 31173149 PMCID: PMC6735853 DOI: 10.1093/toxsci/kfz137] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Revised: 05/28/2019] [Accepted: 05/28/2019] [Indexed: 01/02/2023] Open
Abstract
In adult mouse myocytes, brief exposure to sodium cyanide (CN) in the presence of glucose does not decrease ATP levels, yet produces profound reduction in contractility, intracellular Ca2+ concentration ([Ca2+]i) transient and L-type Ca2+ current (ICa) amplitudes. We analyzed proteomes from myocytes exposed to CN, focusing on ionic currents associated with excitation-contraction coupling. CN induced phosphorylation of α1c subunit of L-type Ca2+ channel and α2 subunit of Na+-K+-ATPase. Methylene blue (MB), a CN antidote that we previously reported to ameliorate CN-induced reduction in contraction, [Ca2+]i transient and ICa amplitudes, was able to reverse this phosphorylation. CN decreased Na+-K+-ATPase current contributed by α2 but not α1 subunit, an effect that was also counteracted by MB. Peptide consensus sequences suggested CN-induced phosphorylation was mediated by protein kinase C epsilon (PKCε). Indeed, CN stimulated PKC kinase activity and induced PKCε membrane translocation, effects that were prevented by MB. Pre-treatment with myristoylated PKCε translocation activator or inhibitor peptides mimicked and inhibited the effects of CN on ICa and myocyte contraction, respectively. We conclude that CN activates PKCε, which phosphorylates L-type Ca2+ channel and Na+-K+-ATPase, resulting in depressed cardiac contractility. We hypothesize that this inhibition of ion fluxes represents a novel mechanism by which the cardiomyocyte reduces its ATP demand (decreased ion fluxes and contractility), diminishes ATP turnover and preserves cell viability. However, this cellular protective effect translates into life-threatening cardiogenic shock in vivo, thereby creating a profound disconnect between survival mechanisms at the cardiomyocyte level from those at the level of the whole organism.
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Affiliation(s)
- Joseph Y Cheung
- Center for Translational Medicine and Lewis Katz School of Medicine of Temple University, Philadelphia, PA.,Department of Medicine, Lewis Katz School of Medicine of Temple University, Philadelphia, PA
| | - Salim Merali
- Moulder Center for Drug Discovery Research, Temple University School of Pharmacy, Philadelphia, PA
| | - JuFang Wang
- Center for Translational Medicine and Lewis Katz School of Medicine of Temple University, Philadelphia, PA
| | - Xue-Qian Zhang
- Center for Translational Medicine and Lewis Katz School of Medicine of Temple University, Philadelphia, PA
| | - Jianliang Song
- Center for Translational Medicine and Lewis Katz School of Medicine of Temple University, Philadelphia, PA
| | - Carmen Merali
- Moulder Center for Drug Discovery Research, Temple University School of Pharmacy, Philadelphia, PA
| | - Dhanendra Tomar
- Center for Translational Medicine and Lewis Katz School of Medicine of Temple University, Philadelphia, PA
| | - Hanning You
- Department of Medicine, Lewis Katz School of Medicine of Temple University, Philadelphia, PA
| | | | - Philippe Haouzi
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, Pennsylvania State University College of Medicine, Hershey, PA
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7
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Hawrysh PJ, Buck LT. Mitochondrial matrix pH acidifies during anoxia and is maintained by the F 1F o-ATPase in anoxia-tolerant painted turtle cortical neurons. FEBS Open Bio 2019; 9:571-581. [PMID: 30984533 PMCID: PMC6443863 DOI: 10.1002/2211-5463.12612] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2018] [Revised: 01/18/2019] [Accepted: 02/05/2019] [Indexed: 12/19/2022] Open
Abstract
The western painted turtle (Chrysemys picta bellii) can survive extended periods of anoxia via a series of mechanisms that serve to reduce its energetic needs. Central to these mechanisms is the response of mitochondria, which depolarize in response to anoxia in turtle pyramidal neurons due to an influx of K+. It is currently unknown how mitochondrial matrix pH is affected by this response and we hypothesized that matrix pH acidifies during anoxia due to increased K+/H+ exchanger activity. Inhibition of K+/H+ exchange via quinine led to a collapse of mitochondrial membrane potential (Ψm) during oxygenated conditions in turtle cortical neurons, as indicated by rhodamine‐123 fluorescence, and this occurred twice as quickly during anoxia which indicates an elevation in K+ conductance. Mitochondrial matrix pH acidified during anoxia, as indicated by SNARF‐1 fluorescence imaged via confocal microscopy, and further acidification occurred during anoxia when the F1Fo‐ATPase was inhibited with oligomycin‐A, indicating that ΔpH collapse is prevented during anoxic conditions. Collectively, these results indicate that the mitochondrial proton electrochemical gradient is actively preserved during anoxia to prevent a collapse of Ψm and ΔpH.
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Affiliation(s)
| | - Leslie Thomas Buck
- Department of Cell and Systems Biology University of Toronto Canada.,Department of Ecology and Evolutionary Biology University of Toronto Canada
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8
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Fanter CE, Lin Z, Keenan SW, Janzen FJ, Mitchell TS, Warren DE. Development-specific transcriptomic profiling suggests new mechanisms for anoxic survival in the ventricle of overwintering turtles. J Exp Biol 2019; 223:jeb.213918. [DOI: 10.1242/jeb.213918] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 12/18/2019] [Indexed: 12/28/2022]
Abstract
Oxygen deprivation swiftly damages tissues in most animals, yet some species show remarkable abilities to tolerate little or even no oxygen. Painted turtles exhibit a development-dependent tolerance that allows adults to survive anoxia ∼4x longer than hatchlings: adults survive ∼170 days and hatchlings survive ∼40 days at 3°C. We hypothesized this difference is related to development-dependent differences in ventricular gene expression. Using a comparative ontogenetic approach, we examined whole transcriptomic changes before, during, and five days after a 20-day bout of anoxic submergence at 3°C. Ontogeny accounted for more gene expression differences than treatment (anoxia or recovery): 1,175 vs. 237 genes, respectively. Of the 237 differences, 93 could confer protection against anoxia and reperfusion injury, 68 could be injurious, and 20 may be constitutively protective. Especially striking during anoxia was the expression pattern of all 76 annotated ribosomal protein (R-protein) mRNAs, which decreased in anoxia-tolerant adults, but increased in anoxia-sensitive hatchlings, suggesting adult-specific regulation of translational suppression. These genes, along with 60 others that decreased their levels in adults and either increased or remained unchanged in hatchlings, implicate antagonistic pleiotropy as a mechanism to resolve the long-standing question about why hatchling painted turtles overwinter in terrestrial nests, rather than emerge and overwinter in water during their first year. In sum, developmental differences in the transcriptome of the turtle ventricle revealed potentially protective mechanisms that contribute to extraordinary adult-specific anoxia tolerance, and provide a unique perspective on differences between the anoxia-induced molecular responses of anoxia-tolerant or anoxia-sensitive phenotypes within a species.
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Affiliation(s)
- Cornelia E. Fanter
- Saint Louis University, Department of Biology, 3507 Laclede Ave., St. Louis, Missouri, 63103, USA
| | - Zhenguo Lin
- Saint Louis University, Department of Biology, 3507 Laclede Ave., St. Louis, Missouri, 63103, USA
| | - Sarah W. Keenan
- South Dakota School of Mines & Technology, Department of Geology and Geological Engineering, 501 East St. Joseph St., Rapid City, South Dakota, 57701, USA
| | - Fredric J. Janzen
- Iowa State University, Department of Ecology, Evolution and Organismal Biology, 251 Bessey Hall, Ames, Iowa, 50011, USA
| | - Timothy S. Mitchell
- University of Minnesota, Department of Ecology, Evolution and Behavior, 1479 Gortner Ave. Saint Paul, MN, 55108, USA
| | - Daniel E. Warren
- Saint Louis University, Department of Biology, 3507 Laclede Ave., St. Louis, Missouri, 63103, USA
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9
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Phosphorylation of the mitochondrial ATP-sensitive potassium channel occurs independently of PKCε in turtle brain. Comp Biochem Physiol B Biochem Mol Biol 2016; 200:44-53. [DOI: 10.1016/j.cbpb.2016.06.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2016] [Revised: 05/26/2016] [Accepted: 06/01/2016] [Indexed: 01/25/2023]
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10
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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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11
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Wijenayake S, Storey KB. The role of DNA methylation during anoxia tolerance in a freshwater turtle (Trachemys scripta elegans). J Comp Physiol B 2016; 186:333-42. [PMID: 26843075 DOI: 10.1007/s00360-016-0960-x] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2015] [Revised: 01/05/2016] [Accepted: 01/15/2016] [Indexed: 11/24/2022]
Abstract
Oxygen deprivation is a lethal stress that only a few animals can tolerate for extended periods. This study focuses on analyzing the role of DNA methylation in aiding natural anoxia tolerance in a champion vertebrate anaerobe, the red-eared slider turtle (Trachemys scripta elegans). We examined the relative expression and total enzymatic activity of four DNA methyltransferases (DNMT1, DNMT2, DNMT3a and DNMT3b), two methyl-binding domain proteins (MBD1 and MBD2), and relative genomic levels of 5-methylcytosine under control, 5 h anoxic, and 20 h anoxic conditions in liver, heart, and white skeletal muscle (n = 4, p < 0.05). In liver, protein expression of DNMT1, DNMT2, MBD1, and MBD2 rose significantly by two- to fourfold after 5 h anoxic submergence compared to normoxic-control conditions. In heart, 5 h anoxia submergence resulted in a 1.4-fold increase in DNMT3a levels and a significant decrease in MBD1 and MBD2 levels to ~30 % of control values. In white muscle, DNMT3a and DNMT3b increased threefold and MBD1 levels increased by 50 % in response to 5 h anoxia. Total DNMT activity rose by 0.6-2.0-fold in liver and white muscle and likewise global 5mC levels significantly increased in liver and white muscle under 5 and 20 h anoxia. The results demonstrate an overall increase in DNA methylation, DNMT protein expression and enzymatic activity in response to 5 and 20 h anoxia in liver and white muscle indicating a potential downregulation of gene expression via this epigenetic mechanism during oxygen deprivation.
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Affiliation(s)
- Sanoji Wijenayake
- Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada
| | - Kenneth B Storey
- Department of Biology, Department of Chemistry, Canada Research Chair in Molecular Physiology, Institute of Biochemistry, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canada.
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12
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Rider MH. Role of AMP-activated protein kinase in metabolic depression in animals. J Comp Physiol B 2015; 186:1-16. [PMID: 26174210 DOI: 10.1007/s00360-015-0920-x] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2015] [Revised: 06/23/2015] [Accepted: 07/01/2015] [Indexed: 01/24/2023]
Abstract
AMP-activated protein kinase (AMPK) is a highly conserved eukaryotic protein serine/threonine kinase that controls cellular and whole body energy homoeostasis. AMPK is activated during energy stress by a rise in AMP:ATP ratio and maintains energy balance by phosphorylating targets to switch on catabolic ATP-generating pathways, while at the same time switching off anabolic ATP-consuming processes. Metabolic depression is a strategy used by many animals to survive environmental stress and has been extensively studied across phylogeny by comparative biochemists and physiologists, but the role of AMPK has only recently been addressed. This review first deals with the evolution of AMPK in eukaryotes (excluding plants and fungi) and its regulation. Changes in adenine nucleotides and AMPK activation are described in animals during environmental energy stress, before considering the involvement of AMPK in controlling β-oxidation, fatty acid synthesis, triacylglycerol mobilization and protein synthesis. Lastly, strategies are presented to validate the role of AMPK in mediating metabolic depression by phosphorylating downstream targets.
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Affiliation(s)
- Mark H Rider
- de Duve Institute and Université Catholique de Louvain, Avenue Hippocrate 75, 1200, Brussels, Belgium.
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13
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Kocha KM, Reilly K, Porplycia DSM, McDonald J, Snider T, Moyes CD. Evolution of the oxygen sensitivity of cytochrome c oxidase subunit 4. Am J Physiol Regul Integr Comp Physiol 2014; 308:R305-20. [PMID: 25519729 DOI: 10.1152/ajpregu.00281.2014] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Vertebrates possess two paralogs of cytochrome c oxidase (COX) subunit 4: a ubiquitous COX4-1 and a hypoxia-linked COX4-2. Mammalian COX4-2 is thought to have a role in relation to fine-tuning metabolism in low oxygen levels, conferred through both structural differences in the subunit protein structure and regulatory differences in the gene. We sought to elucidate the pervasiveness of this feature across vertebrates. The ratio of COX4-2/4-1 mRNA is generally low in mammals, but this ratio was higher in fish and reptiles, particularly turtles. The COX4-2 gene appeared unresponsive to low oxygen in nonmammalian models (zebrafish, goldfish, tilapia, anoles, and turtles) and fish cell lines. Reporter genes constructed from the amphibian and reptile homologues of the mammalian oxygen-responsive elements and hypoxia-responsive elements did not respond to low oxygen. Unlike the rodent ortholog, the promoter of goldfish COX4-2 did not respond to hypoxia or anoxia. The protein sequences of the COX4-2 peptide showed that the disulfide bridge seen in human and rodent orthologs would be precluded in other mammalian lineages and lower vertebrates, all of which lack the requisite pair of cysteines. The coordinating ligands of the ATP-binding site are largely conserved across mammals and reptiles, but in Xenopus and fish, sequence variations may disrupt the ability of the protein to bind ATP at this site. Collectively, these results suggest that many of the genetic and structural features of COX4-2 that impart responsiveness and benefits in hypoxia may be restricted to the Euarchontoglires lineage that includes primates, lagomorphs, and rodents.
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Affiliation(s)
- K M Kocha
- Department of Biology, Queen's University, Kingston, Ontario, Canada
| | - K Reilly
- Department of Biology, Queen's University, Kingston, Ontario, Canada
| | - D S M Porplycia
- Department of Biology, Queen's University, Kingston, Ontario, Canada
| | - J McDonald
- Department of Biology, Queen's University, Kingston, Ontario, Canada
| | - T Snider
- Department of Biology, Queen's University, Kingston, Ontario, Canada
| | - C D Moyes
- Department of Biology, Queen's University, Kingston, Ontario, Canada
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14
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Podrabsky JE, Menze MA, Hand SC. Long-Term survival of anoxia despite rapid ATP decline in embryos of the annual killifish Austrofundulus limnaeus. ACTA ACUST UNITED AC 2012; 317:524-32. [PMID: 22927170 DOI: 10.1002/jez.1744] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2012] [Revised: 05/11/2012] [Accepted: 06/05/2012] [Indexed: 01/24/2023]
Abstract
Embryos of the annual killifish Austrofundulus limnaeus can survive for months in the complete absence of oxygen. Survival of anoxia is associated with entry into a state of metabolic dormancy known as diapause. However, extreme tolerance of anoxia is retained for several days of post-diapause development. Rates of heat dissipation in diapause II and 4 days post-diapause II embryos were measured under aerobic conditions and during the transition into anoxia. Phosphorylated adenylate compounds were quantified in embryos during entry into anoxia and after 12 hr of aerobic recovery. Rates of heat dissipation were not affected by exposure to anoxia in diapause II embryos, while post-diapause II embryos experienced a profound decrease in heat dissipation. ATP decreased substantially in both developmental stages upon exposure to anoxia, and all indicators of cellular energetic status indicated energetic stress, at least based on the mammalian paradigm. The rate of decline in ATP is the most acute reported for any vertebrate. The mechanisms responsible for cellular survival despite a clear dysregulation between energy production and energy consumption remain to be identified. Necrotic and apoptotic cell death in response to hypoxia contribute to poor survival during many diseases and pathological conditions in mammals. Understanding the mechanisms that are in place to prevent maladaptive cell death in embryos of A. limnaeus may greatly improve treatment strategies in diseases that involve hypoxia and reperfusion injuries.
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Affiliation(s)
- Jason E Podrabsky
- Department of Biology, Portland State University, Portland, Oregon 97207-0751, USA.
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15
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Stecyk JAW, Paajanen V, Farrell AP, Vornanen M. Effect of temperature and prolonged anoxia exposure on electrophysiological properties of the turtle (Trachemys scripta) heart. Am J Physiol Regul Integr Comp Physiol 2007; 293:R421-37. [PMID: 17442785 DOI: 10.1152/ajpregu.00096.2007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cardiac activity of the turtle (Trachemys scripta) is greatly depressed with cold acclimation and anoxia. We examined what electrophysiological modifications accompany and perhaps facilitate this depression of cardiac activity. Turtles were first acclimated to 21 degrees C or 5 degrees C and held under either normoxic or anoxic (6 h at 21 degrees C; 14 days at 5 degrees C) conditions. We then measured cardiac action potentials (APs) using spontaneously contracting whole heart preparations and whole cell current densities of sarcolemmal ion channels using isolated ventricular myocytes under appropriate normoxic and anoxic conditions. Compared with 21 degrees C-acclimated turtles, 5 degrees C-acclimated turtles exhibited a less negative resting membrane potential (by 18-29 mV), a 4.7- to 6.8-fold slower AP upstroke rate, and a 4.2- to 4.9-fold greater AP duration. Correspondingly, peak densities of ventricular voltage-gated Na(+) (I(Na)) and L-type Ca(2+) currents and inward slope conductances of inward rectifier K(+) (I(K1)) channel current were approximately 1/7th (Q(10) = 3.4), 1/13th (Q(10) = 5.0), and one-half (Q(10) = 1.4) of those of 21 degrees C-acclimated ventricular myocytes, respectively. With anoxia at 21 degrees C, peak I(Na) density doubled and ventricular AP duration increased by 47%, a change proportional to the reported approximately 30% reduction of intrinsic heart rate. In contrast, with anoxia at 5 degrees C, ventricular AP characteristics were unaffected; of the ion currents investigated, only the inward conductance via I(K1) changed significantly (reduced by 46%). The present findings indicate that cold temperature, more so than prolonged anoxia, results in substantial modifications of cardiac APs and reduction of ventricular ion current densities. These changes likely prepare cardiac muscle for winter anoxia conditions.
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Affiliation(s)
- Jonathan A W Stecyk
- Department of Zoology, University of British Columbia, Vancouver, BC, Canada.
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Pamenter ME, Richards MD, Buck LT. Anoxia-induced changes in reactive oxygen species and cyclic nucleotides in the painted turtle. J Comp Physiol B 2007; 177:473-81. [PMID: 17347830 DOI: 10.1007/s00360-007-0145-8] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2006] [Revised: 12/28/2006] [Accepted: 01/03/2007] [Indexed: 01/07/2023]
Abstract
The Western painted turtle survives months without oxygen. A key adaptation is a coordinated reduction of cellular ATP production and utilization that may be signaled by changes in the concentrations of reactive oxygen species (ROS) and cyclic nucleotides (cAMP and cGMP). Little is known about the involvement of cyclic nucleotides in the turtle's metabolic arrest and ROS have not been previously measured in any facultative anaerobes. The present study was designed to measure changes in these second messengers in the anoxic turtle. ROS were measured in isolated turtle brain sheets during a 40-min normoxic to anoxic transition. Changes in cAMP and cGMP were determined in turtle brain, pectoralis muscle, heart and liver throughout 4 h of forced submergence at 20-22 degrees C. Turtle brain ROS production decreased 25% within 10 min of cyanide or N(2)-induced anoxia and returned to control levels upon reoxygenation. Inhibition of electron transfer from ubiquinol to complex III caused a smaller decrease in [ROS]. Conversely, inhibition of complex I increased [ROS] 15% above controls. In brain [cAMP] decreased 63%. In liver [cAMP] doubled after 2 h of anoxia before returning to control levels with prolonged anoxia. Conversely, skeletal muscle and heart [cAMP] remained unchanged; however, skeletal muscle [cGMP] became elevated sixfold after 4 h of submergence. In liver and heart [cGMP] rose 41 and 127%, respectively, after 2 h of anoxia. Brain [cGMP] did not change significantly during 4 h of submergence. We conclude that turtle brain ROS production occurs primarily between mitochondrial complexes I and III and decreases during anoxia. Also, cyclic nucleotide concentrations change in a manner suggestive of a role in metabolic suppression in the brain and a role in increasing liver glycogenolysis.
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Affiliation(s)
- Matthew Edward Pamenter
- Department of Cell and Systems Biology, University of Toronto, 25 Harbord St., Toronto, ON, Canada M5S 3G5
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17
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Jackson DC, Taylor SE, Asare VS, Villarnovo D, Gall JM, Reese SA. Comparative shell buffering properties correlate with anoxia tolerance in freshwater turtles. Am J Physiol Regul Integr Comp Physiol 2007; 292:R1008-15. [PMID: 17008457 DOI: 10.1152/ajpregu.00519.2006] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Freshwater turtles as a group are more resistant to anoxia than other vertebrates, but some species, such as painted turtles, for reasons not fully understood, can remain anoxic at winter temperatures far longer than others. Because buffering of lactic acid by the shell of the painted turtle is crucial to its long-term anoxic survival, we have tested the hypothesis that previously described differences in anoxia tolerance of five species of North American freshwater turtles may be explained at least in part by differences in their shell composition and buffering capacity. All species tested have large mineralized shells. Shell comparisons included 1) total shell CO2concentration, 2) volume of titrated acid required to hold incubating shell powder at pH 7.0 for 3 h (an indication of buffer release from shell), and 3) lactate concentration of shell samples incubated to equilibrium in a standard lactate solution. For each measurement, the more anoxia-tolerant species (painted turtle, Chrysemys picta; snapping turtle, Chelydra serpentina) had higher values than the less anoxia-tolerant species (musk turtle, Sternotherus odoratus; map turtle, Graptemys geographica; red-eared slider, Trachemys scripta). We suggest that greater concentrations of accessible CO2(as carbonate or bicarbonate) in the more tolerant species enable these species, when acidotic, to release more buffer into the extracellular fluid and to take up more lactic acid into their shells. We conclude that the interspecific differences in shell composition and buffering can contribute to, but cannot explain fully, the variations observed in anoxia tolerance among freshwater turtles.
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Affiliation(s)
- Donald C Jackson
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Box G, Brown University, Providence, RI 02912, USA.
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Gorr TA, Gassmann M, Wappner P. Sensing and responding to hypoxia via HIF in model invertebrates. JOURNAL OF INSECT PHYSIOLOGY 2006; 52:349-64. [PMID: 16500673 DOI: 10.1016/j.jinsphys.2006.01.002] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2005] [Revised: 01/04/2006] [Accepted: 01/05/2006] [Indexed: 05/06/2023]
Abstract
This past decade has brought considerable progress towards elucidating the molecular mechanisms of oxygen sensing pathways by which mammalian cells are able to detect and adjust, or succumb, to hypoxia. In contrast, far less is known about the protein and DNA constituents that endow many invertebrate species to withstand and recover from even more severe and prolonged O2 limitations. In spite of these differences in hypoxia tolerance, inadequacy in oxygen supply is, from mammals to insects to nematodes, signaled onto the DNA level predominantly by hypoxia-inducible factors (HIFs). Across the animal kingdom, HIF accumulates in hypoxic, but not normoxic, cells and functions in a remarkably conserved pathway. Using crustacean (Daphnia magna) and insect (Drosophila melanogaster) models, work by us and others has implicated HIF in restoring O2 delivery via stimulated hemoglobin synthesis (Daphnia) or tracheal remodeling (Drosophila). HIF is essential for these arthropods to adapt and survive during moderate O2 limitations. A similar life-preserving role for HIF-signaling in hypoxic, but not anoxic, environments had previously been established for another stress-tolerant invertebrate model, the nematode Caenorhabditis elegans. Exploring regulations of oxygen-dependent Daphnia and Drosophila genes in cell culture and in vivo have furthermore aided in uncovering novel HIF-targeting mechanisms that might operate to fine-tune the activity of this transcription factor under steadily hypoxic, rather than changing, oxygen tensions. We conclude our review with yet another addition to the growing list of HIF's many functions: the control of cellular growth during fly development.
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Affiliation(s)
- Thomas A Gorr
- Institute of Veterinary Physiology, Vetsuisse Faculty and Zurich Center for Integrative Human Physiology (ZIHP), University of Zurich, Winterthurerstrasse 260, CH-8057, Zurich, Switzerland.
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Abstract
Peter Hochachka was one of the most creative forces in the field of comparative physiology during the past half-century. His career was truly an exploratory adventure, in both intellectual and geographic senses. His broad comparative studies of metabolism in organisms as diverse as trout, tunas, oysters, squid, turtles, locusts, hummingbirds, seals, and humans revealed the adaptable features of enzymes and metabolic pathways that provide the biochemical bases for diverse lifestyles and environments. In its combined breadth and depth, no other corpus of work better illustrates the principle of "unity in diversity" that marks comparative physiology. Through his publications, his stimulating mentorship, his broad editorial services, and his continuous-and highly infectious-enthusiasm for his field, Peter Hochachka served as one of the most influential leaders in the transformation of comparative physiology.
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Affiliation(s)
- George N Somero
- Department of Biological Sciences, Hopkins Marine Station, Stanford University, Pacific Grove, California 93950-3094, USA.
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Reese SA, Ultsch GR, Jackson DC. Lactate accumulation, glycogen depletion, and shell composition of hatchling turtles during simulated aquatic hibernation. J Exp Biol 2004; 207:2889-95. [PMID: 15235017 DOI: 10.1242/jeb.01124] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
We submerged hatchling western painted turtles Chrysemys pictaSchneider, snapping turtles Chelydra serpentina L. and map turtles Graptemys geographica Le Sueur in normoxic and anoxic water at 3°C. Periodically, turtles were removed and whole-body [lactate] and[glycogen] were measured along with relative shell mass, shell water, and shell ash. We analyzed the shell for [Na+], [K+], total calcium, total magnesium, Pi and total CO2. All three species were able to tolerate long-term submergence in normoxic water without accumulating any lactate, indicating sufficient extrapulmonary O2extraction to remain aerobic even after 150 days. Survival in anoxic water was 15 days in map turtles, 30 days in snapping turtles, and 40 days in painted turtles. Survival of hatchlings was only about one third the life of their adult conspecifics in anoxic water. Much of the decrease in survival was attributable to a dramatically lower shell-bone content (44% ash in adult painted turtles vs. 3% ash in hatchlings of all three species) and a smaller buffer content of bone (1.3 mmol g–1 CO2in adult painted turtles vs. 0.13–0.23 mmol g–1 CO2 in hatchlings of the three species). The reduced survivability of turtle hatchlings in anoxic water requires that hatchlings either avoid aquatic hibernacula that may become severely hypoxic or anoxic (snapping turtles), or overwinter terrestrially (painted turtles and map turtles).
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Affiliation(s)
- Scott A Reese
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, Rhode Island 02912, USA.
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21
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Abstract
Many freshwater turtles in temperate climates may experience winter periods trapped under ice unable to breathe, in anoxic mud, or in water depleted of O(2). To survive, these animals must not only retain function while anoxic, but they must do so for extended periods of time. Two general physiological adaptive responses appear to underlie this capacity for long-term survival. The first is a coordinated depression of metabolic processes within the cells, both the glycolytic pathway that produces ATP and the cellular processes, such as ion pumping, that consume ATP. As a result, both the rate of substrate depletion and the rate of lactic acid production are slowed greatly. The second is an exploitation of the extensive buffering capacity of the turtle's shell and skeleton to neutralize the large amount of lactic acid that eventually accumulates. Two separate shell mechanisms are involved: release of carbonate buffers from the shell and uptake of lactic acid into the shell where it is buffered and sequestered. Together, the metabolic and buffering mechanisms permit animals to survive for 3-4 months at 3 degrees C with no O(2) and with circulating lactate levels of 150 mmol l(-1) or more.
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Affiliation(s)
- Donald C Jackson
- Department of Molecular Pharmacology, Physiology and Biotechnology, Brown University, Providence, RI 02912, USA.
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Bishop T, St-Pierre J, Brand MD. Primary causes of decreased mitochondrial oxygen consumption during metabolic depression in snail cells. Am J Physiol Regul Integr Comp Physiol 2002; 282:R372-82. [PMID: 11792646 DOI: 10.1152/ajpregu.00401.2001] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cells isolated from the hepatopancreas of estivating snails (Helix aspersa) have strongly depressed mitochondrial respiration compared with controls. Mitochondrial respiration was divided into substrate oxidation (which produces the mitochondrial membrane potential) and ATP turnover and proton leak (which consume it). The activity of substrate oxidation (and probably ATP turnover) decreased, whereas the activity of proton leak remained constant in estivation. These primary changes resulted in a lower mitochondrial membrane potential in hepatopancreas cells from estivating compared with active snails, leading to secondary decreases in respiration to drive ATP turnover and proton leak. The respiration to drive ATP turnover and proton leak decreased in proportion to the overall decrease in mitochondrial respiration, so that the amount of ATP turned over per O2 consumed remained relatively constant and aerobic efficiency was maintained in this hypometabolic state. At least 75% of the total response of mitochondrial respiration to estivation was caused by primary changes in the kinetics of substrate oxidation, with only 25% or less of the response occurring through primary effects on ATP turnover.
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Affiliation(s)
- Tammie Bishop
- Medical Research Council, Dunn Human Nutrition Unit, Cambridge CB2 2XY, United Kingdom.
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Abstract
SUMMARYMost animals experience some degree of hypoxia and hypothermia during the course of their natural life history either as a consequence of ambient ‘exposure’ per se or through metabolic, respiratory and/or circulatory insufficiency. A prevailing experimental approach has been to probe tissues from natural models of hypoxia-tolerant and cold-tolerant vertebrates to look for common mechanisms of defence against O2 lack and hypothermia. The ability to sustain vital cellular functions in severe cases of either condition varies widely amongst the vertebrates. Like humans, the vast majority of mammals are unable to survive prolonged periods of hypothermia or O2 deprivation owing to irreversible membrane damage and loss of cellular ion homeostasis in vital organs such as the brain and heart. However, numerous hibernating endotherms, neonatal and diving mammals as well as many ectotherms can tolerate prolonged periods that would, in clinical terms, be called asphyxia or deep hypothermia. The key to their survival under such conditions lies in an inherent ability to downregulate their cellular metabolic rate to new hypometabolic steady states in a way that balances the ATP demand and ATP supply pathways.
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Affiliation(s)
- R G Boutilier
- Department of Zoology, Downing Street, Cambridge CB2 3EJ, UK.
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Guppy M, Reeves DC, Bishop T, Withers P, Buckingham JA, Brand MD. Intrinsic metabolic depression in cells isolated from the hepatopancreas of estivating snails. FASEB J 2000; 14:999-1004. [PMID: 10783155 DOI: 10.1096/fasebj.14.7.999] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Many animals across the phylogenetic scale are routinely capable of depressing their metabolic rate to 5-15% of that at rest, remaining in this state sometimes for years. However, despite its widespread occurrence, the biochemical processes associated with metabolic depression remain obscure. We demonstrate here the development of an isolated cell model for the study of metabolic depression. The isolated cells from the hepatopancreas (digestive gland) of the land snail (Helix aspersa) are oxygen conformers; i.e., their rate of respiration depends on pO(2). Cells isolated from estivating snails show a stable metabolic depression to 30% of control (despite the long and invasive process of cell isolation) when metabolic rate at the physiological pH and pO(2) of the hemolymph of estivating snails is compared with metabolic rate at the physiological pH and pO(2) of the hemolymph of control snails. When the extrinsic effects of pH and pO(2) are excluded, the intrinsic metabolic depression of the cells from estivating snails is still to below 50% of control snails. The in vitro effect of pO(2) on metabolic rate is independent of pH and state (awake or estivating), but the effects of pH and state significantly interact. This suggests that pH and state change affect metabolic depression by similar mechanisms but that the metabolic depression by hypoxia involves a separate mechanism.
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Affiliation(s)
- M Guppy
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1QW, UK.
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Land SC, Hochachka PW. A heme-protein-based oxygen-sensing mechanism controls the expression and suppression of multiple proteins in anoxia-tolerant turtle hepatocytes. Proc Natl Acad Sci U S A 1995; 92:7505-9. [PMID: 11607568 PMCID: PMC41368 DOI: 10.1073/pnas.92.16.7505] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The O2 sensitivity of protein expression was assessed in hepatocytes from the western painted turtle. Anoxic cells consistently expressed proteins of 83.0, 70.4, 42.5, 35.3, and 16.1 kDa and suppressed proteins of 63.7, 48.2, 36.9, 29.5, and 17.7 kDa. Except for the 70.4-kDa protein, this pattern was absent during aerobic incubation with 2 mM NaCN, suggesting a specific requirement for O2. Aerobic incubation with Co2+ or Ni2+ increased expression of the 42.5-, 35.3-, and 16.1-kDa protein bands which was diminished with the heme synthesis inhibitor 4,6-dioxoheptanoic acid. Proteins suppressed in anoxia were also suppressed during aerobic incubation with Co2+ or Ni2+ but this was not relieved by 4,6-dioxoheptanoic acid. The anoxia- and Co2+/Ni2+-induced expression of the 42.5-, 35.3-, and 16.1-kDa protein bands was antagonized by 10% CO; however, with the exception of the 17.7-kDa protein, this was not found for any of the O2- or Co2+/Ni2+-suppressed proteins. Anoxia-induced proteins were compared with proteins expressed during heat shock. Heat shock proteins appeared at 90.2, 74.8, 63.4, 25, and 15.5 kDa and were of distinct molecular masses compared with the anoxia-induced proteins. These results suggest that O2-sensing mechanisms are active in the control of protein expression and suppression during anoxia and that, in the case of the 42.5-, 35.3-, 17.7-, and 16.1-kDa proteins, a conformational change in a ferro-heme protein is involved in transducing the O2 signal.
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Affiliation(s)
- S C Land
- Department of Zoology, University of British Columbia, Vancouver, BC Canada V6T 1Z4
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Tretyakov AV, Farber HW. Endothelial cell tolerance to hypoxia. Potential role of purine nucleotide phosphates. J Clin Invest 1995; 95:738-44. [PMID: 7860755 PMCID: PMC295542 DOI: 10.1172/jci117721] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The ability of cells to tolerate hypoxia is critical to their survival, but varies greatly among different cell types. Despite alterations in many cellular responses during hypoxic exposure, pulmonary arterial endothelial cells (PAEC) retain their viability and cellular integrity. Under similar experimental conditions, other cell types, exemplified by renal tubular epithelial cells, are extremely hypoxia sensitive and are rapidly and irreversibly damaged. To investigate potential mechanisms by which PAEC maintain cellular and functional integrity under these conditions, we compared the turnover of adenine and guanine nucleotides in hypoxia tolerant PAEC and in hypoxia-sensitive renal tubular endothelial cells under various hypoxic conditions. Under several different hypoxic conditions, hypoxia-tolerant PAEC maintained or actually increased ATP levels and the percentage of these nucleotides found in the high energy phosphates, ATP and GTP. In contrast, in hypoxia-sensitive renal tubular endothelial cells, the same high energy phosphates were rapidly depleted. Yet, in both cell types, there were minor alterations in the uptake of the precusor nucleotide and its incorporation into the appropriate purine nucleotide phosphates and marked decreases in ATPase and GTPase activity. This maintenance of high energy phosphates in hypoxic PAEC suggests that there exists tight regulation of ATP and GTP turnover in these cells and that preservation of these nucleotides may contribute to the tolerance of PAEC to acute and chronic hypoxia.
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Affiliation(s)
- A V Tretyakov
- Pulmonary Center, Boston University School of Medicine, Massachusetts 02118
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