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Andersen NCM, Fago A, Damsgaard C. Evolution of hemoglobin function in tropical air-breathing catfishes. JOURNAL OF EXPERIMENTAL ZOOLOGY. PART A, ECOLOGICAL AND INTEGRATIVE PHYSIOLOGY 2021; 335:814-819. [PMID: 34254462 DOI: 10.1002/jez.2504] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Revised: 06/18/2021] [Accepted: 06/23/2021] [Indexed: 11/08/2022]
Abstract
The evolution of hemoglobin function in the transition from water- to air-breathing has been highly debated but remains unresolved. Here, we characterized the hemoglobin function in five closely related water- and air-breathing catfishes. We identify distinct directions of hemoglobin evolution in the clades that evolved air-breathing, and we show strong selection on hemoglobin function within the catfishes. These findings show that the lack of a general direction in hemoglobin function in the transition from water- to air-breathing may have resulted from divergent selection on hemoglobin function in independent clades of air-breathing fishes.
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Affiliation(s)
| | - Angela Fago
- Section for Zoophysiology, Department of Biology, Aarhus University, Aarhus C, Denmark
| | - Christian Damsgaard
- Section for Zoophysiology, Department of Biology, Aarhus University, Aarhus C, Denmark.,Aarhus Institute of Advanced Studies, Aarhus University, Aarhus C, Denmark
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2
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Abstract
Hibernation is a powerful response of a number of mammalian species to reduce energy during the cold winter season, when food is scarce. Mammalian hibernators survive winter by spending most of the time in a state of torpor, where basal metabolic rate is strongly suppressed and body temperature comes closer to ambient temperature. These torpor bouts are regularly interrupted by short arousals, where metabolic rate and body temperature spontaneously return to normal levels. The mechanisms underlying these changes, and in particular the strong metabolic suppression of torpor, have long remained elusive. As summarized in this Commentary, increasing evidence points to a potential key role for hydrogen sulfide (H2S) in the suppression of mitochondrial respiration during torpor. The idea that H2S could be involved in hibernation originated in some early studies, where exogenous H2S gas was found to induce a torpor-like state in mice, and despite some controversy, the idea persisted. H2S is a widespread signaling molecule capable of inhibiting mitochondrial respiration in vitro and studies found significant in vivo changes in endogenous H2S metabolites associated with hibernation or torpor. Along with increased expression of H2S-synthesizing enzymes during torpor, H2S degradation catalyzed by the mitochondrial sulfide:quinone oxidoreductase (SQR) appears to have a key role in controlling H2S availability for inhibiting respiration. Specifically, in thirteen-lined squirrels, SQR is highly expressed and inhibited in torpor, possibly by acetylation, thereby limiting H2S oxidation and causing inhibition of respiration. H2S may also control other aspects associated with hibernation, such as synthesis of antioxidant enzymes and of SQR itself.
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Affiliation(s)
| | - Angela Fago
- Department of Biology, Aarhus University, Aarhus C 8000, Denmark
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3
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González-Bernardo E, Russo LF, Valderrábano E, Fernández Á, Penteriani V. Denning in brown bears. Ecol Evol 2020; 10:6844-6862. [PMID: 32724555 PMCID: PMC7381752 DOI: 10.1002/ece3.6372] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Revised: 04/16/2020] [Accepted: 04/22/2020] [Indexed: 12/12/2022] Open
Abstract
Hibernation represents an adaptation for coping with unfavorable environmental conditions. For brown bears Ursus arctos, hibernation is a critical period as pronounced temporal reductions in several physiological functions occur.Here, we review the three main aspects of brown bear denning: (1) den chronology, (2) den characteristics, and (3) hibernation physiology in order to identify (a) proximate and ultimate factors of hibernation as well as (b) research gaps and conservation priorities.Den chronology, which varies by sex and reproductive status, depends on environmental factors, such as snow, temperature, food availability, and den altitude. Significant variation in hibernation across latitudes occurs for both den entry and exit.The choice of a den and its surroundings may affect individual fitness, for example, loss of offspring and excessive energy consumption. Den selection is the result of broad- and fine-scale habitat selection, mainly linked to den insulation, remoteness, and availability of food in the surroundings of the den location.Hibernation is a metabolic challenge for the brown bears, in which a series of physiological adaptations in tissues and organs enable survival under nutritional deprivation, maintain high levels of lipids, preserve muscle, and bone and prevent cardiovascular pathologies such as atherosclerosis. It is important to understand: (a) proximate and ultimate factors in denning behavior and the difference between actual drivers of hibernation (i.e., factors to which bears directly respond) and their correlates; (b) how changes in climatic factors might affect the ability of bears to face global climate change and the human-mediated changes in food availability; (c) hyperphagia (period in which brown bears accumulate fat reserves), predenning and denning periods, including for those populations in which bears do not hibernate every year; and (d) how to approach the study of bear denning merging insights from different perspectives, that is, physiology, ecology, and behavior.
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Affiliation(s)
- Enrique González-Bernardo
- Research Unit of Biodiversity (UMIB, CSIC-UO-PA) Mieres Spain
- Pyrenean Institute of Ecology (IPE-CSIC) Zaragoza Spain
| | - Luca Francesco Russo
- Research Unit of Biodiversity (UMIB, CSIC-UO-PA) Mieres Spain
- Department of Biosciences and the Territory Università degli Studi del Molise Pesche Italy
| | - Esther Valderrábano
- COPAR Research Group Faculty of Veterinary University of Santiago de Compostela Lugo Spain
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4
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Fröbert O, Frøbert AM, Kindberg J, Arnemo JM, Overgaard MT. The brown bear as a translational model for sedentary lifestyle-related diseases. J Intern Med 2020; 287:263-270. [PMID: 31595572 DOI: 10.1111/joim.12983] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Sedentary lifestyle accelerates biological ageing, is a major risk factor for developing metabolic syndrome and is associated with cardiovascular disease, diabetes mellitus, kidney failure, sarcopenia and osteoporosis. In contrast to the linear path to worsening health in humans with metabolic syndrome, brown bears have developed a circular metabolic plasticity enabling these animals to tolerate obesity and a 'sedentary lifestyle' during hibernation and exit the den metabolically healthy in spring. Bears are close to humans physiology wise, much closer than rodents, the preferred experimental animals in medical research, and may better serve as translational model to develop treatments for lifestyle-related diseases. In this review, aspects of brown bear hibernation survival strategies are outlined and conceivable experimental strategies to learn from bears are described.
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Affiliation(s)
- O Fröbert
- Department of Cardiology, Faculty of Health, Örebro University, Örebro, Sweden
| | - A M Frøbert
- Department of Chemistry and Bioscience, Aalborg University, Aalborg, Denmark
| | - J Kindberg
- Department of Wildlife, Fish and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden.,Norwegian Institute for Nature Research, Trondheim, Norway
| | - J M Arnemo
- Department of Forestry and Wildlife Management, Inland Norway University of Applied Sciences, Koppang, Norway
| | - M T Overgaard
- Department of Chemistry and Bioscience, Aalborg University, Aalborg, Denmark
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5
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Regulation of blood oxygen transport in hibernating mammals. J Comp Physiol B 2017; 187:847-856. [DOI: 10.1007/s00360-017-1085-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2016] [Revised: 12/19/2016] [Accepted: 03/07/2017] [Indexed: 12/23/2022]
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6
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Tarahovsky YS, Fadeeva IS, Komelina NP, Khrenov MO, Zakharova NM. Antipsychotic inductors of brain hypothermia and torpor-like states: perspectives of application. Psychopharmacology (Berl) 2017; 234:173-184. [PMID: 27933367 DOI: 10.1007/s00213-016-4496-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Accepted: 11/26/2016] [Indexed: 12/12/2022]
Abstract
Hypothermia and hypometabolism (hypometabothermia) normally observed during natural hibernation and torpor, allow animals to protect their body and brain against the damaging effects of adverse environment. A similar state of hypothermia can be achieved under artificial conditions through physical cooling or pharmacological effects directed at suppression of metabolism and the processes of thermoregulation. In these conditions called torpor-like states, the mammalian ability to recover from stroke, heart attack, and traumatic injuries greatly increases. Therefore, the development of therapeutic methods for different pathologies is a matter of great concern. With the discovery of the antipsychotic drug chlorpromazine in the 1950s of the last century, the first attempts to create a pharmacologically induced state of hibernation for therapeutic purposes were made. That was the beginning of numerous studies in animals and the broad use of therapeutic hypothermia in medicine. Over the last years, many new agents have been discovered which were capable of lowering the body temperature and inhibiting the metabolism. The psychotropic agents occupy a significant place among them, which, in our opinion, is not sufficiently recognized in the contemporary literature. In this review, we summarized the latest achievements related to the ability of modern antipsychotics to target specific receptors in the brain, responsible for the initiation of hypometabothermia.
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Affiliation(s)
- Yury S Tarahovsky
- Institute of Cell Biophysics RAS, Pushchino, Moscow Region, Russian Federation, 142290. .,Institute of Theoretical and Experimental Biophysics RAS, Pushchino, Moscow Region, Russian Federation, 142290.
| | - Irina S Fadeeva
- Institute of Cell Biophysics RAS, Pushchino, Moscow Region, Russian Federation, 142290.,Institute of Theoretical and Experimental Biophysics RAS, Pushchino, Moscow Region, Russian Federation, 142290
| | - Natalia P Komelina
- Institute of Cell Biophysics RAS, Pushchino, Moscow Region, Russian Federation, 142290
| | - Maxim O Khrenov
- Institute of Cell Biophysics RAS, Pushchino, Moscow Region, Russian Federation, 142290
| | - Nadezhda M Zakharova
- Institute of Cell Biophysics RAS, Pushchino, Moscow Region, Russian Federation, 142290
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7
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Welinder KG, Hansen R, Overgaard MT, Brohus M, Sønderkær M, von Bergen M, Rolle-Kampczyk U, Otto W, Lindahl TL, Arinell K, Evans AL, Swenson JE, Revsbech IG, Frøbert O. Biochemical Foundations of Health and Energy Conservation in Hibernating Free-ranging Subadult Brown Bear Ursus arctos. J Biol Chem 2016; 291:22509-22523. [PMID: 27609515 DOI: 10.1074/jbc.m116.742916] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Revised: 09/02/2016] [Indexed: 12/12/2022] Open
Abstract
Brown bears (Ursus arctos) hibernate for 5-7 months without eating, drinking, urinating, and defecating at a metabolic rate of only 25% of the summer activity rate. Nonetheless, they emerge healthy and alert in spring. We quantified the biochemical adaptations for hibernation by comparing the proteome, metabolome, and hematological features of blood from hibernating and active free-ranging subadult brown bears with a focus on conservation of health and energy. We found that total plasma protein concentration increased during hibernation, even though the concentrations of most individual plasma proteins decreased, as did the white blood cell types. Strikingly, antimicrobial defense proteins increased in concentration. Central functions in hibernation involving the coagulation response and protease inhibition, as well as lipid transport and metabolism, were upheld by increased levels of very few key or broad specificity proteins. The changes in coagulation factor levels matched the changes in activity measurements. A dramatic 45-fold increase in sex hormone-binding globulin levels during hibernation draws, for the first time, attention to its significant but unknown role in maintaining hibernation physiology. We propose that energy for the costly protein synthesis is reduced by three mechanisms as follows: (i) dehydration, which increases protein concentration without de novo synthesis; (ii) reduced protein degradation rates due to a 6 °C reduction in body temperature and decreased protease activity; and (iii) a marked redistribution of energy resources only increasing de novo synthesis of a few key proteins. The comprehensive global data identified novel biochemical strategies for bear adaptations to the extreme condition of hibernation and have implications for our understanding of physiology in general.
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Affiliation(s)
- Karen Gjesing Welinder
- From the Department of Chemistry and Bioscience, Section of Biotechnology, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg East, Denmark,
| | - Rasmus Hansen
- From the Department of Chemistry and Bioscience, Section of Biotechnology, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg East, Denmark
| | - Michael Toft Overgaard
- From the Department of Chemistry and Bioscience, Section of Biotechnology, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg East, Denmark
| | - Malene Brohus
- From the Department of Chemistry and Bioscience, Section of Biotechnology, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg East, Denmark
| | - Mads Sønderkær
- From the Department of Chemistry and Bioscience, Section of Biotechnology, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg East, Denmark
| | - Martin von Bergen
- From the Department of Chemistry and Bioscience, Section of Biotechnology, Aalborg University, Fredrik Bajers Vej 7H, 9220 Aalborg East, Denmark.,the Departments of Metabolomics and.,Proteomics, Helmholtz Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany
| | | | - Wolfgang Otto
- Proteomics, Helmholtz Centre for Environmental Research (UFZ), Permoserstrasse 15, 04318 Leipzig, Germany
| | - Tomas L Lindahl
- the Department of Clinical and Experimental Medicine, Linköping University, 581 85 Linköping, Sweden
| | - Karin Arinell
- the Department of Cardiology, Faculty of Health, Örebro University, 701 85 Örebro, Sweden
| | - Alina L Evans
- the Department of Forestry and Wildlife Management, Hedmark University College, Campus Evenstrand, 2411 Elverum, Norway
| | - Jon E Swenson
- the Department for Ecology and Natural Resource Management, Norwegian University of Life Sciences, Postbox 5014, 1432 Ås, Norway.,the Norwegian Institute for Nature Research, Tungasletta 2, N-7485 Trondheim, Norway, and
| | - Inge G Revsbech
- the Department of Bioscience, Zoophysiology, Aarhus University, C.F. Møllers Allé 3, 8000 Aarhus C, Denmark
| | - Ole Frøbert
- the Department of Cardiology, Faculty of Health, Örebro University, 701 85 Örebro, Sweden
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8
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Berg von Linde M, Arevström L, Fröbert O. Insights from the Den: How Hibernating Bears May Help Us Understand and Treat Human Disease. Clin Transl Sci 2015; 8:601-5. [PMID: 26083277 DOI: 10.1111/cts.12279] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Hibernating brown bears (Ursus arctos) and black bears (Ursus americanus) spend half of the year in a physically inactive state inside their winter dens without food intake and defecating and no or little urination. Under similar extreme conditions, humans would suffer from loss of lean body mass, heart failure, thrombosis, azotemia, osteoporosis, and more. However, bears exit the den in the spring strong without organ injuries. Translational animal models are used in human medicine but traditional experimental animals have several shortcomings; thus, we believe that it is time to systematically explore new models. In this review paper, we describe physiological adaptations of hibernating bears and how similar adaptations in humans could theoretically alleviate medical conditions. The bear has solved most of the health challenges faced by humans, including heart and kidney disease, atherosclerosis and thrombosis, and muscle wasting and osteoporosis. Understanding and applying this library of information could lead to a number of major discoveries that could have implications for the understanding and treatment of human disease.
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Affiliation(s)
| | - Lilith Arevström
- Department of Cardiology, Faculty of Health, Örebro University, Orebro, Sweden
| | - Ole Fröbert
- Department of Cardiology, Faculty of Health, Örebro University, Orebro, Sweden
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9
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Nelson OL, Robbins CT. Cardiovascular function in large to small hibernators: bears to ground squirrels. J Comp Physiol B 2014; 185:265-79. [PMID: 25542162 DOI: 10.1007/s00360-014-0881-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Revised: 11/25/2014] [Accepted: 12/02/2014] [Indexed: 01/19/2023]
Abstract
Mammalian hibernation has intrigued scientists due to extreme variations in normal seasonal physiological homeostasis. Numerous species manifest a hibernation phenotype although the characteristics of the hypometabolic state can be quite different. Ground squirrels (e.g., Sciuridae) are often considered the prototypical hibernator as individuals in this genus transition from an active, euthermic state (37 °C) to a nonresponsive hibernating state where torpid body temperature commonly falls to 3-5 °C. However, the hibernating state is not continuous as periodic warming and arousals occur. In contrast, the larger hibernators of genus Ursus are less hypothermic (body temperatures decline from approximately 37°-33 °C), are more reactive, and cyclical arousals do not occur. Both species dramatically reduce cardiac output during hibernation from the active state (bears ~75 % reduction in bears and ~97 % reduction in ground squirrels), and both species demonstrate hypokinetic atrial chamber activity. However, there are several important differences in cardiac function between the two groups during hibernation. Left ventricular diastolic filling volumes and stroke volumes do not differ in bears between seasons, but increased diastolic and stroke volumes during hibernation are important contributors to cardiac output in ground squirrels. Decreased cardiac muscle mass and increased ventricular stiffness have been found in bears, whereas ground squirrels have increased cardiac muscle mass and decreased ventricular stiffness during hibernation. Molecular pathways of cardiac muscle plasticity reveal differences between the species in the modification of sarcomeric proteins such as titin and α myosin heavy chain during hibernation. The differences in hibernation character are likely to account for the alternative cardiac phenotypes and functional strategies manifested by the two species. Molecular investigation coupled with better knowledge of seasonal physiological alterations is dramatically advancing our understanding of small and large hibernators and their evolutionary differences.
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Affiliation(s)
- O Lynne Nelson
- Department of Veterinary Clinical Sciences, Washington State University, 100 Grimes Way, Pullman, WA, 99164, USA,
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10
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Revsbech IG, Shen X, Chakravarti R, Jensen FB, Thiel B, Evans AL, Kindberg J, Fröbert O, Stuehr DJ, Kevil CG, Fago A. Hydrogen sulfide and nitric oxide metabolites in the blood of free-ranging brown bears and their potential roles in hibernation. Free Radic Biol Med 2014; 73:349-57. [PMID: 24909614 PMCID: PMC4413933 DOI: 10.1016/j.freeradbiomed.2014.05.025] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Revised: 05/19/2014] [Accepted: 05/30/2014] [Indexed: 02/08/2023]
Abstract
During winter hibernation, brown bears (Ursus arctos) lie in dens for half a year without eating while their basal metabolism is largely suppressed. To understand the underlying mechanisms of metabolic depression in hibernation, we measured type and content of blood metabolites of two ubiquitous inhibitors of mitochondrial respiration, hydrogen sulfide (H2S) and nitric oxide (NO), in winter-hibernating and summer-active free-ranging Scandinavian brown bears. We found that levels of sulfide metabolites were overall similar in summer-active and hibernating bears but their composition in the plasma differed significantly, with a decrease in bound sulfane sulfur in hibernation. High levels of unbound free sulfide correlated with high levels of cysteine (Cys) and with low levels of bound sulfane sulfur, indicating that during hibernation H2S, in addition to being formed enzymatically from the substrate Cys, may also be regenerated from its oxidation products, including thiosulfate and polysulfides. In the absence of any dietary intake, this shift in the mode of H2S synthesis would help preserve free Cys for synthesis of glutathione (GSH), a major antioxidant found at high levels in the red blood cells of hibernating bears. In contrast, circulating nitrite and erythrocytic S-nitrosation of glyceraldehyde-3-phosphate dehydrogenase, taken as markers of NO metabolism, did not change appreciably. Our findings reveal that remodeling of H2S metabolism and enhanced intracellular GSH levels are hallmarks of the aerobic metabolic suppression of hibernating bears.
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Affiliation(s)
- Inge G Revsbech
- Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark
| | - Xinggui Shen
- Department of Pathology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA
| | - Ritu Chakravarti
- Department of Pathobiology, Cleveland Clinic Lerner Research Institute, Cleveland, OH 44195, USA
| | - Frank B Jensen
- Department of Biology, University of Southern Denmark, 5230 Odense M, Denmark
| | - Bonnie Thiel
- Department of Medicine, Case Western Reserve University, Cleveland, OH 44106, USA
| | - Alina L Evans
- Department of Forestry and Wildlife Management, Faculty of Applied Ecology and Agricultural Sciences, Hedmark University College, Campus Evenstad, 2418 Elverum, Norway
| | - Jonas Kindberg
- Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, 90183 Umeå, Sweden
| | - Ole Fröbert
- Department of Cardiology, Örebro University Hospital, 70362 Örebro, Sweden
| | - Dennis J Stuehr
- Department of Pathobiology, Cleveland Clinic Lerner Research Institute, Cleveland, OH 44195, USA
| | - Christopher G Kevil
- Department of Pathology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA
| | - Angela Fago
- Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
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11
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Revsbech IG, Tufts DM, Projecto-Garcia J, Moriyama H, Weber RE, Storz JF, Fago A. Hemoglobin function and allosteric regulation in semi-fossorial rodents (family Sciuridae) with different altitudinal ranges. ACTA ACUST UNITED AC 2014; 216:4264-71. [PMID: 24172889 DOI: 10.1242/jeb.091397] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Semi-fossorial ground squirrels face challenges to respiratory gas transport associated with the chronic hypoxia and hypercapnia of underground burrows, and such challenges are compounded in species that are native to high altitude. During hibernation, such species must also contend with vicissitudes of blood gas concentrations and plasma pH caused by episodic breathing. Here, we report an analysis of hemoglobin (Hb) function in six species of marmotine ground squirrels with different altitudinal distributions. Regardless of their native altitude, all species have high Hb-O2 affinities, mainly due to suppressed sensitivities to allosteric effectors [2,3-diphosphoglycerate (DPG) and chloride ions]. This suppressed anion sensitivity is surprising given that all canonical anion-binding sites are conserved. Two sciurid species, the golden-mantled and thirteen-lined ground squirrel, have Hb-O2 affinities that are characterized by high pH sensitivity and low thermal sensitivity relative to the Hbs of humans and other mammals. The pronounced Bohr effect is surprising in light of highly unusual amino acid substitutions at the C-termini that are known to abolish the Bohr effect in human HbA. Taken together, the high O2 affinity of sciurid Hbs suggests an enhanced capacity for pulmonary O2 loading under hypoxic and hypercapnic conditions, while the large Bohr effect should help to ensure efficient O2 unloading in tissue capillaries. In spite of the relatively low thermal sensitivities of the sciurid Hbs, our results indicate that the effect of hypothermia on Hb oxygenation is the main factor contributing to the increased blood-O2 affinity in hibernating ground squirrels.
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Affiliation(s)
- Inge G Revsbech
- Zoophysiology, Department of Bioscience, Aarhus University, C.F. Møllers Allè 3, DK-8000 Aarhus C, Denmark
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12
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Damsgaard C, Storz JF, Hoffmann FG, Fago A. Hemoglobin isoform differentiation and allosteric regulation of oxygen binding in the turtle, Trachemys scripta. Am J Physiol Regul Integr Comp Physiol 2013; 305:R961-7. [PMID: 23986362 PMCID: PMC3798770 DOI: 10.1152/ajpregu.00284.2013] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Accepted: 08/20/2013] [Indexed: 01/09/2023]
Abstract
When freshwater turtles acclimatize to winter hibernation, there is a gradual transition from aerobic to anaerobic metabolism, which may require adjustments of blood O2 transport before turtles become anoxic. Here, we report the effects of protons, anionic cofactors, and temperature on the O2-binding properties of isolated hemoglobin (Hb) isoforms, HbA and HbD, in the turtle Trachemys scripta. We determined the primary structures of the constituent subunits of the two Hb isoforms, and we related the measured functional properties to differences in O2 affinity between untreated hemolysates from turtles that were acclimated to normoxia and anoxia. Our data show that HbD has a consistently higher O2 affinity compared with HbA, whereas Bohr and temperature effects, as well as thiol reactivity, are similar. Although sequence data show amino acid substitutions at two known β-chain ATP-binding site positions, we find high ATP affinities for both Hb isoforms, suggesting an alternative and stronger binding site for ATP. The high ATP affinities indicate that, although ATP levels decrease in red blood cells of turtles acclimating to anoxia, the O2 affinity would remain largely unchanged, as confirmed by O2-binding measurements of untreated hemolysates from normoxic and anoxic turtles. Thus, the increase in blood-O2 affinity that accompanies winter acclimation is mainly attributable to a decrease in temperature rather than in concentrations of organic phosphates. This is the first extensive study on freshwater turtle Hb isoforms, providing molecular evidence for adaptive changes in O2 transport associated with acclimation to severe hypoxia.
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