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Gershman A, Hauck Q, Dick M, Jamison JM, Tassia M, Agirrezabala X, Muhammad S, Ali R, Workman RE, Valle M, Wong GW, Welch KC, Timp W. Genomic insights into metabolic flux in hummingbirds. Genome Res 2023; 33:703-714. [PMID: 37156619 PMCID: PMC10317124 DOI: 10.1101/gr.276779.122] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2022] [Accepted: 04/26/2023] [Indexed: 05/10/2023]
Abstract
Hummingbirds are very well adapted to sustain efficient and rapid metabolic shifts. They oxidize ingested nectar to directly fuel flight when foraging but have to switch to oxidizing stored lipids derived from ingested sugars during the night or long-distance migratory flights. Understanding how this organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. To explore these questions, we generated a chromosome-scale genome assembly of the ruby-throated hummingbird (A. colubris) using a combination of long- and short-read sequencing, scaffolding it using existing assemblies. We then used hybrid long- and short-read RNA sequencing of liver and muscle tissue in fasted and fed metabolic states for a comprehensive transcriptome assembly and annotation. Our genomic and transcriptomic data found positive selection of key metabolic genes in nectivorous avian species and deletion of critical genes (SLC2A4, GCK) involved in glucostasis in other vertebrates. We found expression of a fructose-specific version of SLC2A5 putatively in place of insulin-sensitive SLC2A5, with predicted protein models suggesting affinity for both fructose and glucose. Alternative isoforms may even act to sequester fructose to preclude limitations from transport in metabolism. Finally, we identified differentially expressed genes from fasted and fed hummingbirds, suggesting key pathways for the rapid metabolic switch hummingbirds undergo.
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Affiliation(s)
- Ariel Gershman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
- Department of Molecular Biology and Genetics, Johns Hopkins University, Baltimore, Maryland 21287, USA
| | - Quinn Hauck
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Morag Dick
- Cell & Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada
| | - Jerrica M Jamison
- Cell & Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada
| | - Michael Tassia
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
| | - Xabier Agirrezabala
- CIC bioGUNE, Basque Research and Technology Alliance (BRTA), 48160 Derio, Spain
| | - Saad Muhammad
- Cell & Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada
| | - Raafay Ali
- Cell & Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada
| | - Rachael E Workman
- Department of Molecular Biology and Genetics, Johns Hopkins University, Baltimore, Maryland 21287, USA
| | - Mikel Valle
- CIC bioGUNE, Basque Research and Technology Alliance (BRTA), 48160 Derio, Spain
| | - G William Wong
- Department of Physiology and Center for Metabolism and Obesity Research, School of Medicine, The Johns Hopkins University, Baltimore, Maryland 21205, USA
| | - Kenneth C Welch
- Cell & Systems Biology, University of Toronto, Toronto, Ontario M5S 3G5, Canada
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, M1C 1A4, Canada
| | - Winston Timp
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA;
- Department of Molecular Biology and Genetics, Johns Hopkins University, Baltimore, Maryland 21287, USA
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2
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Cockburn G, Ko MC, Sadanandan KR, Miller ET, Nakagita T, Monte A, Cho S, Roura E, Toda Y, Baldwin MW. Synergism, Bifunctionality, and the Evolution of a Gradual Sensory Trade-off in Hummingbird Taste Receptors. Mol Biol Evol 2022; 39:msab367. [PMID: 34978567 PMCID: PMC8826506 DOI: 10.1093/molbev/msab367] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022] Open
Abstract
Sensory receptor evolution can imply trade-offs between ligands, but the extent to which such trade-offs occur and the underlying processes shaping their evolution is not well understood. For example, hummingbirds have repurposed their ancestral savory receptor (T1R1-T1R3) to detect sugars, but the impact of this sensory shift on amino acid perception is unclear. Here, we use functional and behavioral approaches to show that the hummingbird T1R1-T1R3 acts as a bifunctional receptor responsive to both sugars and amino acids. Our comparative analyses reveal substantial functional diversity across the hummingbird radiation and suggest an evolutionary timeline for T1R1-T1R3 retuning. Finally, we identify a novel form of synergism between sugars and amino acids in vertebrate taste receptors. This work uncovers an unexplored axis of sensory diversity, suggesting new ways in which nectar chemistry and pollinator preferences can coevolve.
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Affiliation(s)
- Glenn Cockburn
- Evolution of Sensory Systems Research Group, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Meng-Ching Ko
- Evolution of Sensory Systems Research Group, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Keren R Sadanandan
- Evolution of Sensory Systems Research Group, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Eliot T Miller
- Macaulay Library, Cornell Lab of Ornithology, Ithaca, NY, USA
| | - Tomoya Nakagita
- Department of Agricultural Chemistry, School of Agriculture, Meiji University, Kawasaki, Kanagawa, Japan
- Proteo-Science Center, Ehime University, Matsuyama, Ehime, Japan
| | - Amanda Monte
- Department of Behavioral Neurobiology, Max Planck Institute for Ornithology, Seewiesen, Germany
| | - Sungbo Cho
- Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, Australia
| | - Eugeni Roura
- Centre for Nutrition and Food Sciences, Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, St Lucia, Australia
| | - Yasuka Toda
- Department of Agricultural Chemistry, School of Agriculture, Meiji University, Kawasaki, Kanagawa, Japan
| | - Maude W Baldwin
- Evolution of Sensory Systems Research Group, Max Planck Institute for Ornithology, Seewiesen, Germany
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3
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Liang RJ, Taylor S, Nahiyaan N, Song J, Murphy CJ, Dantas E, Cheng S, Hsu TW, Ramsamooj S, Grover R, Hwang SK, Ngo B, Cantley LC, Rhee KY, Goncalves MD. GLUT5 (SLC2A5) enables fructose-mediated proliferation independent of ketohexokinase. Cancer Metab 2021; 9:12. [PMID: 33762003 PMCID: PMC7992954 DOI: 10.1186/s40170-021-00246-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2020] [Accepted: 02/08/2021] [Indexed: 12/23/2022] Open
Abstract
BACKGROUND Fructose is an abundant source of carbon and energy for cells to use for metabolism, but only certain cell types use fructose to proliferate. Tumor cells that acquire the ability to metabolize fructose have a fitness advantage over their neighboring cells, but the proteins that mediate fructose metabolism in this context are unknown. Here, we investigated the determinants of fructose-mediated cell proliferation. METHODS Live cell imaging and crystal violet assays were used to characterize the ability of several cell lines (RKO, H508, HepG2, Huh7, HEK293T (293T), A172, U118-MG, U87, MCF-7, MDA-MB-468, PC3, DLD1 HCT116, and 22RV1) to proliferate in fructose (i.e., the fructolytic ability). Fructose metabolism gene expression was determined by RT-qPCR and western blot for each cell line. A positive selection approach was used to "train" non-fructolytic PC3 cells to utilize fructose for proliferation. RNA-seq was performed on parental and trained PC3 cells to find key transcripts associated with fructolytic ability. A CRISPR-cas9 plasmid containing KHK-specific sgRNA was transfected in 293T cells to generate KHK-/- cells. Lentiviral transduction was used to overexpress empty vector, KHK, or GLUT5 in cells. Metabolic profiling was done with seahorse metabolic flux analysis as well as LC/MS metabolomics. Cell Titer Glo was used to determine cell sensitivity to 2-deoxyglucose in media containing either fructose or glucose. RESULTS We found that neither the tissue of origin nor expression level of any single gene related to fructose catabolism determine the fructolytic ability. However, cells cultured chronically in fructose can develop fructolytic ability. SLC2A5, encoding the fructose transporter, GLUT5, was specifically upregulated in these cells. Overexpression of GLUT5 in non-fructolytic cells enabled growth in fructose-containing media across cells of different origins. GLUT5 permitted fructose to flux through glycolysis using hexokinase (HK) and not ketohexokinase (KHK). CONCLUSIONS We show that GLUT5 is a robust and generalizable driver of fructose-dependent cell proliferation. This indicates that fructose uptake is the limiting factor for fructose-mediated cell proliferation. We further demonstrate that cellular proliferation with fructose is independent of KHK.
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Affiliation(s)
- Roger J Liang
- Division of Endocrinology, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Samuel Taylor
- Division of Endocrinology, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
- Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, New York, NY, 10065, USA
- Weill Cornell/Rockefeller/Sloan Kettering Tri-I MD-PhD program, New York, NY, 10065, USA
| | - Navid Nahiyaan
- Division of Infectious Diseases, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Junho Song
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Charles J Murphy
- Center for Molecular Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, 10065, USA
- Department of Pathology, Memorial Sloan Kettering Cancer Center, New York, NY, 10065, USA
| | - Ezequiel Dantas
- Division of Endocrinology, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Shuyuan Cheng
- Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Ting-Wei Hsu
- Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Shakti Ramsamooj
- Division of Endocrinology, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Rahul Grover
- Weill Cornell Medical College, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Seo-Kyoung Hwang
- Division of Endocrinology, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Bryan Ngo
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
- Weill Cornell Graduate School of Medical Sciences, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Lewis C Cantley
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Kyu Y Rhee
- Division of Infectious Diseases, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Marcus D Goncalves
- Division of Endocrinology, Weill Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA.
- Meyer Cancer Center, Department of Medicine, Weill Cornell Medicine, New York, NY, 10065, USA.
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Zhao X, Li X, Shi X, Karpac J. Diet-MEF2 interactions shape lipid droplet diversification in muscle to influence Drosophila lifespan. Aging Cell 2020; 19:e13172. [PMID: 32537848 PMCID: PMC7433001 DOI: 10.1111/acel.13172] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2020] [Revised: 04/05/2020] [Accepted: 05/05/2020] [Indexed: 12/12/2022] Open
Abstract
The number, size, and composition of lipid droplets can be influenced by dietary changes that shift energy substrate availability. This diversification of lipid droplets can promote metabolic flexibility and shape cellular stress responses in unique tissues with distinctive metabolic roles. Using Drosophila, we uncovered a role for myocyte enhancer factor 2 (MEF2) in modulating diet-dependent lipid droplet diversification within adult striated muscle, impacting mortality rates. Muscle-specific attenuation of MEF2, whose chronic activation maintains glucose and mitochondrial homeostasis, leads to the accumulation of large, cholesterol ester-enriched intramuscular lipid droplets in response to high calorie, carbohydrate-sufficient diets. The diet-dependent accumulation of these lipid droplets also correlates with both enhanced stress protection in muscle and increases in organismal lifespan. Furthermore, MEF2 attenuation releases an antagonistic regulation of cell cycle gene expression programs, and up-regulation of Cyclin E is required for diet- and MEF2-dependent diversification of intramuscular lipid droplets. The integration of MEF2-regulated gene expression networks with dietary responses thus plays a critical role in shaping muscle metabolism and function, further influencing organismal lifespan. Together, these results highlight a potential protective role for intramuscular lipid droplets during dietary adaptation.
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Affiliation(s)
- Xiao Zhao
- Department of Molecular and Cellular MedicineTexas A&M University Health Science CenterBryanTXUSA
| | - Xiaotong Li
- Department of Molecular and Cellular MedicineTexas A&M University Health Science CenterBryanTXUSA
| | - Xiangyu Shi
- Department of Molecular and Cellular MedicineTexas A&M University Health Science CenterBryanTXUSA
| | - Jason Karpac
- Department of Molecular and Cellular MedicineTexas A&M University Health Science CenterBryanTXUSA
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5
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Metabolic Fates of Evening Crop-Stored Sugar in Ruby-Throated Hummingbirds (Archilochus colubris). DIVERSITY-BASEL 2019. [DOI: 10.3390/d11010009] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
During the day, hummingbirds quickly metabolize floral nectar to fuel high metabolic demands, but are unable to feed at night. Though stored fat is the primary nocturnal metabolic fuel, it has been suggested that hummingbirds store nectar in their crop to offset fat expenditure in the night or to directly fuel their first foraging trip in the morning. We examine the use of crop-stored sugar in the nocturnal energy budget of ruby-throated hummingbirds (Archilochus colubris) using respirometry and 13C stable isotope analysis. Hummingbirds were fed a 13C-enriched sugar solution before lights-out and held in respirometry chambers overnight without food. Respirometry results indicate that the hummingbirds metabolized the sugar in the evening meal in less than 2 h, and subsequently primarily catabolized fat. Breath stable isotope signatures provide the key insight that the hummingbirds converted a substantial portion of an evening meal to fats, which they later catabolized to support their overnight metabolism and spare endogenous energy stores. These results show that the value of a hummingbird’s evening meal depends on how much of this energy was converted to fat. Furthermore, this suggests that evening hyperphagia is an important energy maximization strategy, especially during energetically expensive periods such as migration or incubation.
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6
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Workman RE, Myrka AM, Wong GW, Tseng E, Welch KC, Timp W. Single-molecule, full-length transcript sequencing provides insight into the extreme metabolism of the ruby-throated hummingbird Archilochus colubris. Gigascience 2018; 7:1-12. [PMID: 29618047 PMCID: PMC5869288 DOI: 10.1093/gigascience/giy009] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 02/07/2018] [Indexed: 01/09/2023] Open
Abstract
Background Hummingbirds oxidize ingested nectar sugars directly to fuel foraging but cannot sustain this fuel use during fasting periods, such as during the night or during long-distance migratory flights. Instead, fasting hummingbirds switch to oxidizing stored lipids that are derived from ingested sugars. The hummingbird liver plays a key role in moderating energy homeostasis and this remarkable capacity for fuel switching. Additionally, liver is the principle location of de novo lipogenesis, which can occur at exceptionally high rates, such as during premigratory fattening. Yet understanding how this tissue and whole organism moderates energy turnover is hampered by a lack of information regarding how relevant enzymes differ in sequence, expression, and regulation. Findings We generated a de novo transcriptome of the hummingbird liver using PacBio full-length cDNA sequencing (Iso-Seq), yielding 8.6Gb of sequencing data, or 2.6M reads from 4 different size fractions. We analyzed data using the SMRTAnalysis v3.1 Iso-Seq pipeline, then clustered isoforms into gene families to generate de novo gene contigs using Cogent. We performed orthology analysis to identify closely related sequences between our transcriptome and other avian and human gene sets. Finally, we closely examined homology of critical lipid metabolism genes between our transcriptome data and avian and human genomes. Conclusions We confirmed high levels of sequence divergence within hummingbird lipogenic enzymes, suggesting a high probability of adaptive divergent function in the hepatic lipogenic pathways. Our results leverage cutting-edge technology and a novel bioinformatics pipeline to provide a first direct look at the transcriptome of this incredible organism.
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Affiliation(s)
- Rachael E Workman
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland
| | - Alexander M Myrka
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada and Department of Cell & Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - G William Wong
- Department of Physiology and Center for Metabolism and Obesity Research, Johns Hopkins University School of Medicine, Baltimore, Maryland
| | | | - Kenneth C Welch
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada and Department of Cell & Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Winston Timp
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland
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“Alternative” fuels contributing to mitochondrial electron transport: Importance of non-classical pathways in the diversity of animal metabolism. Comp Biochem Physiol B Biochem Mol Biol 2018; 224:185-194. [DOI: 10.1016/j.cbpb.2017.11.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2017] [Revised: 11/08/2017] [Accepted: 11/10/2017] [Indexed: 12/19/2022]
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8
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Myrka AM, Welch KC. Evidence of high transport and phosphorylation capacity for both glucose and fructose in the ruby-throated hummingbird (Archilochus colubris). Comp Biochem Physiol B Biochem Mol Biol 2018; 224:253-261. [DOI: 10.1016/j.cbpb.2017.10.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2017] [Revised: 10/26/2017] [Accepted: 10/31/2017] [Indexed: 02/06/2023]
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9
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Welch KC, Myrka AM, Ali RS, Dick MF. The Metabolic Flexibility of Hovering Vertebrate Nectarivores. Physiology (Bethesda) 2018; 33:127-137. [DOI: 10.1152/physiol.00001.2018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Foraging hummingbirds and nectar bats oxidize both glucose and fructose from nectar at exceptionally high rates. Rapid sugar flux is made possible by adaptations to digestive, cardiovascular, and metabolic physiology affecting shared and distinct pathways for the processing of each sugar. Still, how these animals partition and regulate the metabolism of each sugar and whether this occurs differently between hummingbirds and bats remain unclear.
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Affiliation(s)
- Kenneth C. Welch
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada
- Department of Cell & Systems Biology, University of Toronto, Toronto, Ontario, Canada
- Center for the Neurobiology of Stress, University of Toronto Scarborough, Toronto, Ontario, Canada
| | - Alexander M. Myrka
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada
- Department of Cell & Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Raafay Syed Ali
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada
- Department of Cell & Systems Biology, University of Toronto, Toronto, Ontario, Canada
| | - Morag F. Dick
- Department of Biological Sciences, University of Toronto Scarborough, Toronto, Ontario, Canada
- Department of Cell & Systems Biology, University of Toronto, Toronto, Ontario, Canada
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10
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Sugar Metabolism in Hummingbirds and Nectar Bats. Nutrients 2017; 9:nu9070743. [PMID: 28704953 PMCID: PMC5537857 DOI: 10.3390/nu9070743] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2017] [Revised: 07/03/2017] [Accepted: 07/04/2017] [Indexed: 12/15/2022] Open
Abstract
Hummingbirds and nectar bats coevolved with the plants they visit to feed on floral nectars rich in sugars. The extremely high metabolic costs imposed by small size and hovering flight in combination with reliance upon sugars as their main source of dietary calories resulted in convergent evolution of a suite of structural and functional traits. These allow high rates of aerobic energy metabolism in the flight muscles, fueled almost entirely by the oxidation of dietary sugars, during flight. High intestinal sucrase activities enable high rates of sucrose hydrolysis. Intestinal absorption of glucose and fructose occurs mainly through a paracellular pathway. In the fasted state, energy metabolism during flight relies on the oxidation of fat synthesized from previously-ingested sugar. During repeated bouts of hover-feeding, the enhanced digestive capacities, in combination with high capacities for sugar transport and oxidation in the flight muscles, allow the operation of the “sugar oxidation cascade”, the pathway by which dietary sugars are directly oxidized by flight muscles during exercise. It is suggested that the potentially harmful effects of nectar diets are prevented by locomotory exercise, just as in human hunter-gatherers who consume large quantities of honey.
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McCue MD, Welch KC. (13)C-Breath testing in animals: theory, applications, and future directions. J Comp Physiol B 2015; 186:265-85. [PMID: 26660654 DOI: 10.1007/s00360-015-0950-4] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2015] [Revised: 11/11/2015] [Accepted: 11/25/2015] [Indexed: 10/22/2022]
Abstract
The carbon isotope values in the exhaled breath of an animal mirror the carbon isotope values of the metabolic fuels being oxidized. The measurement of stable carbon isotopes in carbon dioxide is called (13)C-breath testing and offers a minimally invasive method to study substrate oxidation in vivo. (13)C-breath testing has been broadly used to study human exercise, nutrition, and pathologies since the 1970s. Owing to reduced use of radioactive isotopes and the increased convenience and affordability of (13)C-analyzers, the past decade has witnessed a sharp increase in the use of breath testing throughout comparative physiology--especially to answer questions about how and when animals oxidize particular nutrients. Here, we review the practical aspects of (13)C-breath testing and identify the strengths and weaknesses of different methodological approaches including the use of natural abundance versus artificially-enriched (13)C tracers. We critically compare the information that can be obtained using different experimental protocols such as diet-switching versus fuel-switching. We also discuss several factors that should be considered when designing breath testing experiments including extrinsic versus intrinsic (13)C-labelling and different approaches to model nutrient oxidation. We use case studies to highlight the myriad applications of (13)C-breath testing in basic and clinical human studies as well as comparative studies of fuel use, energetics, and carbon turnover in multiple vertebrate and invertebrate groups. Lastly, we call for increased and rigorous use of (13)C-breath testing to explore a variety of new research areas and potentially answer long standing questions related to thermobiology, locomotion, and nutrition.
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12
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Welch KC, Péronnet F, Hatch KA, Voigt CC, McCue MD. Carbon stable-isotope tracking in breath for comparative studies of fuel use. Ann N Y Acad Sci 2015; 1365:15-32. [PMID: 25817456 DOI: 10.1111/nyas.12737] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Almost half a century ago, researchers demonstrated that the ratio of stable carbon isotopes in exhaled breath of rats and humans could reveal the oxidation of labeled substrates in vivo, opening a new chapter in the study of fuel use, the fate of ingested substrates, and aerobic metabolism. Until recently, the combined use of respirometry and stable-isotope tracer techniques had not been broadly employed to study fuel use in other animal groups. In this review, we summarize the history of this approach in human and animal research and define best practices that maximize its utility. We also summarize several case studies that use stable-isotope measurements of breath to explore the limits of aerobic metabolism and substrate turnover among several species and various physiological states. We highlight the importance of a comparative approach in revealing the profound effects that phylogeny, ecology, and behavior can have in shaping aerobic metabolism and energetics as well as the fundamental biological principles that underlie fuel use and metabolic function across taxa. New analytical equipment and refinement of methodology make the combined use of respirometry and stable-isotope tracer techniques simpler to perform, less costly, and more field ready than ever before.
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Affiliation(s)
- Kenneth C Welch
- Department of Biology, University of Toronto Scarborough, Toronto, Ontario, Canada
| | - François Péronnet
- Département de Kinésiologie, Université de Montréal, Montréal, Québec, Canada
| | - Kent A Hatch
- Department of Biology, Long Island University Post, Brookville, New York
| | - Christian C Voigt
- Department of Evolutionary Ecology, Leibniz Institute for Zoo and Wildlife Research, Berlin, Germany
| | - Marshall D McCue
- Department of Biological Sciences, St. Mary's University, San Antonio, Texas
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