High-Throughput Tissue Bioenergetics Analysis Reveals Identical Metabolic Allometric Scaling for Teleost Hearts and Whole Organisms

RESEARCH ARTICLE High-Throughput Tissue Bioenergetics Analysis Reveals Identical Metabolic Allometric Scaling for Teleost Hearts and Whole Organisms Nishad Jayasundara1*, Jordan S. Kozal1, Mariah C. Arnold1, Sherine S. L. Chan2, Richard T. Di Giulio1 1 Nicholas School of the Environment, Duke University, Durham, North Carolina, United States of America, 2 Medical University of South Carolina, Charleston, South Carolina, United States of America * Abstract OPEN ACCESS Citation: Jayasundara N, Kozal JS, Arnold MC, Chan SSL, Di Giulio RT (2015) High-Throughput Tissue Bioenergetics Analysis Reveals Identical Metabolic Allometric Scaling for Teleost Hearts and Whole Organisms. PLoS ONE 10(9): e0137710. doi:10.1371/journal.pone.0137710 Editor: Jianhua Zhang, University of Alabama at Birmingham, UNITED STATES Received: April 23, 2015 Accepted: August 21, 2015 Published: September 14, 2015 Copyright: © 2015 Jayasundara et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: Data used for regression analysis comparing whole fish, heart and brain basal, and maximal metabolic rates are included in the Supporting Information file and other data contained within the paper. Funding: The Di Giulio lab is supported by National Institutes of Environmental Health awards P42ES010356 (Duke University Superfund Research Center) and Duke University Program in Environmental Health Training grant (T32ES021432). Purchase of the XFe24 Extracellular Flux Analyzer was supported by funds provided by the Organismal metabolic rate, a fundamental metric in biology, demonstrates an allometric scaling relationship with body size. Fractal-like vascular distribution networks of biological systems are proposed to underlie metabolic rate allometric scaling laws from individual organisms to cells, mitochondria, and enzymes. Tissue-specific metabolic scaling is notably absent from this paradigm. In the current study, metabolic scaling relationships of hearts and brains with body size were examined by improving on a high-throughput whole-organ oxygen consumption rate (OCR) analysis method in five biomedically and environmentally relevant teleost model species. Tissue-specific metabolic scaling was compared with organismal routine metabolism (RMO2), which was measured using whole organismal respirometry. Basal heart OCR and organismal RMO2 scaled identically with body mass in a species-specific fashion across all five species tested. However, organismal maximum metabolic rates (MMO2) and pharmacologically-induced maximum cardiac metabolic rates in zebrafish Danio rerio did not show a similar relationship with body mass. Brain metabolic rates did not scale with body size. The identical allometric scaling of heart and organismal metabolic rates with body size suggests that hearts, the power generator of an organism’s vascular distribution network, might be crucial in determining teleost metabolic rate scaling under routine conditions. Furthermore, these findings indicate the possibility of measuring heart OCR utilizing the high-throughput approach presented here as a proxy for organismal metabolic rate—a useful metric in characterizing organismal fitness. In addition to heart and brain OCR, the current approach was also used to measure whole liver OCR, partition cardiac mitochondrial bioenergetic parameters using pharmacological agents, and estimate heart and brain glycolytic rates. This high-throughput whole-organ bioenergetic analysis method has important applications in toxicology, evolutionary physiology, and biomedical sciences, particularly in the context of investigating pathogenesis of mitochondrial diseases. PLOS ONE | DOI:10.1371/journal.pone.0137710 September 14, 2015 1 / 19 Metabolic Scaling of Fish Hearts Office of Research Support and the Nicholas School of the Environment, Duke University. The Chan lab is supported by NIH awards P20RR024485/P20 GM103542, R21DA037706, and R01GM111672. Competing Interests: The authors have declared that no competing interests exist. Introduction The metabolic rate, often characterized as the rate of oxygen consumption, is a fundamental metric in physiological, ecological and evolutionary analyses of organismal survival and fitness. The metabolic rate of an organism demonstrates an allometric scaling relationship with body mass according to the equation Y = a Mb, where Y is metabolic rate, M is body mass, a is the species-specific scaling constant, and b is the scaling exponent [1–4]. The metabolic theory of ecology describes the biological significance of this relationship and provides a framework to predict how allometric scaling of metabolic rate versus body mass governs ecological processes at all levels of organization from individual organisms to the biosphere [5]. The scaling exponent b recently has received widespread attention with West and colleagues [6–8] suggesting that fractal-like vascular distribution networks of biological systems underlie the allometric scaling laws for individual organisms, single cells, intact mitochondria, and enzyme molecules [9]. However, tissue-specific metabolic rate scaling relationships and their correlations with whole organismal metabolic rates are notably absent from this paradigm. In the current study, we improved on a method developed by Little and Seebacher [10] to examine ex vivo heart-specific oxygen consumption rate (OCR) using the XFe24 Extracellular Flux Analyzer (Seahorse Bioscience, Billerica, MA) to explore (i) metabolic rate scaling of heart and brain tissues with organ size and body size and (ii) how these scaling relationships compare with whole organismal metabolic rates in five biomedically and environmentally relevant teleost model species— zebrafish (Danio rerio), Atlantic killifish (Fundulus heteroclitus), mosquito fish (Gambusia holbrooki), Japanese medaka (Oryzias latipes), and fathead minnow (Pimephales promelas). To investigate the metabolic scaling relationship between basal tissue-specific OCR and routine whole organismal metabolic rate (RMO2), we quantified whole organismal respiration rates for each fish prior to heart and brain measurements in all five species. In addition to quantifying basal OCR for tissues, the XFe24 Extracellular Flux Analyzer can be used to obtain indices of tissue-specific mitochondrial bioenergetics with judicious use of different pharmacological agents [10,11]. Interest in mitochondrial function assessments is increasing in many contexts, ranging from biomedical sciences and toxicology to evolutionary and ecological physiology, as mitochondria play an essential role in aerobic ATP production and are involved in a number of other cellular processes [12–14]. Changes in mitochondrial structure and function are associated with a number of metabolic di (...truncated)