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ABSTRACT: Patterns of fuel use during locomotion are determined by exercise intensity and duration, and are remarkably similar across many mammalian taxa. However, as lipids have a high yield of ATP per mole and are stored in large quantities, their use should be favored in endurance-adapted animals. To examine the capacity for alteration or differential regulation of fuel-use patterns, we studied two lines of mice that had been selectively bred for high voluntary wheel running (HR), including one characterized by small hindlimb muscles (HR(mini)) and one without this phenotype (HR(normal)), as well as a nonselected control line. We evaluated: 1) maximal aerobic capacity (Vo(2 max)); 2) whole body fuel use during exercise by indirect calorimetry; 3) cardiac properties; and 4) many factors involved in regulating lipid use. HR mice achieved an increased Vo(2 max) compared with control mice, potentially in part due to HR cardiac capacities for metabolic fuel oxidation and the larger relative heart size of HR(mini) mice. HR mice also exhibited enhanced whole body lipid oxidation rates at 66% Vo(2 max), but HR(mini), HR(normal), and control mice did not differ in the proportional mix of fuels sustaining exercise (% total Vo(2)). However, HR(mini) gastrocnemius muscle had elevated fatty acid translocase (FAT/CD36) sarcolemmal protein and cellular mRNA, fatty acid binding protein (H-FABP) cytosolic protein, peroxisome proliferator-activated receptor (PPAR) α mRNA, and mass-specific activities of citrate synthase, β-hydroxyacyl-CoA dehydrogenase, and hexokinase. Therefore, high-running mouse lines had whole body fuel oxidation rates commensurate with maximal aerobic capacity, despite notable differences in skeletal muscle metabolic phenotypes.
AJP Regulatory Integrative and Comparative Physiology 05/2012; 303(1):R101-11. · 3.34 Impact Factor
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ABSTRACT: Exercise under acute hypoxia elicits a large increase in blood lactate concentration ([La](b)) compared with normoxic exercise. However, several studies in humans show that with the transition to chronic hypoxia, exercise [La](b) returns to normoxic levels. Although extensively examined over the last decades, the muscle-specific mechanisms responsible for this phenomenon remain unknown. To assess the changes in skeletal muscle associated with a transition from acute to chronic hypoxia, CD-1 mice were exposed for 24 h (24H), 1 wk (1WH), or 4 wk (4WH) to hypobaric hypoxia (equivalent to 4,300 m), exercised under 12% O(2), and compared with normoxic mice (N) at 21% O(2). Since the enzyme pyruvate dehydrogenase (PDH) plays a major role in the metabolic fate of pyruvate (oxidation vs. lactate production), we assessed the changes in its activity and regulation. Here we report that when run under hypoxia, 24H mice exhibited the highest blood and intramuscular lactate of all groups, while the 1WH group approached N group values. Concomitantly, the 24H group exhibited the lowest PDH activity, associated with a higher phosphorylation (inactive) state of the Ser(232) residue of PDH, a site specific to PDH kinase-1 (PDK1). Furthermore, protein levels of PDK1 and its regulator, the hypoxia inducible factor-1α (HIF-1α), were both elevated in the 24H group compared with N and 1WH groups. Overall, our results point to a novel mechanism in muscle where the HIF-1α pathway is desensitized in the transition from acute to chronic hypoxia, leading to a reestablishment of PDH activity and a reduction in lactate production by the exercising muscles.
AJP Regulatory Integrative and Comparative Physiology 07/2011; 301(4):R1098-104. · 3.34 Impact Factor
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ABSTRACT: In mammals, environmental challenges often result in physical and metabolic cardiac remodeling (i.e., hypertrophy and a shift from lipid to carbohydrate oxidation). While chronic hypoxia and cold are both known to elicit cardiac changes, little is known about their combined effects.
To investigate the cumulated effects of these two stressors on cardiac physiology, CD-1 mice were exposed for 4 weeks to normoxia/normothermia, hypoxia, cold, or combined hypoxic-cold. We assessed physical characteristics, left ventricular activities of fatty acid catabolic enzymes short-chain β-hydroxyacyl-CoA dehydrogenase (SCHAD) and medium-chain acyl-CoA dehydrogenase, and mRNA levels of Acadm, muscle- and liver-type carnitine palmitoyltransferase (Cpt-1β, Cpt-1α), and the transcriptional regulator PPARα.
1) Chronic hypoxia reduced SCHAD activity without physical remodeling or mRNA changes; 2) chronic cold lead to reduced SCHAD activity in hypertrophied left ventricles and lowered right ventricular Cpt-1α mRNA (compared to chronic hypoxia); and 3) despite causing hypertrophy of both ventricles, chronic exposure to combined hypoxic-cold did not induce significant metabolic remodeling.
In response to environmental challenges, cardiac muscles 1) show distinct physical and metabolic remodeling, 2) respond to two stressors simultaneously but not additively, and 3) maintain an adult metabolic phenotype with long-term exposure to environmentally realistic hypoxic-cold.
Biochimica et Biophysica Acta 12/2010; 1800(12):1248-55. · 4.66 Impact Factor
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ABSTRACT: Many small mammals thermoregulate through shivering in muscle and/or non-shivering thermogenesis (NST) via brown adipose tissue (BAT) by the actions of mitochondrial uncoupling proteins (UCPs). An up-regulation of these mechanisms would be advantageous in a cold environment but not in conditions of low oxygen as it leads to needless increases in energy expenditure. We examined the chronic effect of 4 weeks of exposure to hypobaric hypoxia (H, 480 mm Hg), cold (C, 5 degrees C) and the combination of the two stressors (HC) compared to normoxic thermoneutral controls (N, 28 degrees C) in male CD-1 mice. We found that hypoxic/cold acclimated mice had significantly lower body temperatures (T(b)) after acclimation along with complete abolishment of diurnal T(b) fluctuations. Capacity for NST was assessed by changes in intrascapular BAT mass, mitochondrial content and UCP1 content per milligram mitochondria. Acclimation caused distinct remodeling of BAT that was reflected in differences in NE-induced increases in oxygen consumption (VO(2)) used to assess NST capacity. Reduction of T(b) in HC acclimated mice was not due to a decreased heat-generating capacity of BAT. VO(2) during an acute temperature challenge (32 to 4 degrees C) in normoxia was similar in all treatment groups compared to controls but thermal conductance was greater in C acclimated mice and T(b) higher in HC acclimated mice. We propose that an overriding inhibition by hypoxia on neural feedback pathways persists even after weeks of acclimation when combined with chronic cold.
Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology 11/2010; 157(3):301-9. · 1.61 Impact Factor
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ABSTRACT: The enzyme carnitine palmitoyltransferase (CPT) I is a major regulator of mitochondrial fatty acid oxidation in vertebrates. Numerous genome duplication events throughout evolution have given rise to three (in mammals) or multiple (in fish) genetically and functionally different isoforms of this enzyme. In particular, these isoforms represent a diversification of kinetic and regulatory properties stemming from mutations at the genomic and proteomic levels. Phylogenetic reconstructions reveal a comprehensive view of the CPT I family in vertebrates and genomic modifications leading to structural changes in proteins and functional differences between tissues and taxa. In a model fish species (rainbow trout), the presence of five CPT I isoforms suggests repeated duplication events in bony fishes and salmonids. Subsequently, an array of nucleotide and amino acid substitutions in the isoforms may contribute to a tissue-specific and a previously observed species-specific difference in the IC(50) for malonyl-CoA. Moreover, all five isoforms are expressed in trout at the mRNA level in skeletal muscle, heart, liver, kidney, and intestine. In general, transcript levels of the beta-isoforms were higher in muscle tissues, while levels of the alpha-isoforms were higher in other tissues. Rainbow trout also exhibit developmental plasticity in relative mRNA expression of CPT I isoforms from fry to juvenile to adult stage. Thus the evolution of CPT I has resulted in a very diverse family of isoforms. These differences represent a degree of specificity in the ability of species to regulate function at the protein and tissue levels, which, in turn, may allow for precise control of lipid oxidation in individual tissues during physiological perturbations.
AJP Regulatory Integrative and Comparative Physiology 08/2010; 299(2):R579-89. · 3.34 Impact Factor
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ABSTRACT: This is the first study to implement a genomic approach to ascertain both transcriptional and functional end points of chronic Cu toxicity in fish associated with experimentally manipulated water chemistries. Over 21 d, zebrafish acclimated to softwater (Na(+) = 0.06 mM, Ca(2+) = 0.08 mM, Mg(2+) = 0.03 mM) were exposed to the following: soft-water (Ctrl); 12 microg L(-1) Cu (Cu); 3.3 mM Na(+) (Na); 3.3 mM Na(+) + 12 microg L(-1) Cu (Na + Cu); 3.3 mM Ca(2+) (Ca); or 3.3 mM Ca(2+) + 12 microg L(-1) Cu (Ca + Cu). Although effective at reducing Cu load in all tissues, Na(+) in the presence of Cu did not decrease the degree of oxidative damage, particularly in the gill and gut. In contrast, Ca + Cu treatment decreased Cu accumulation in gill, but not liver or gut, with no reduction in oxidative damage. Transcriptional analysis of candidate genes (atp7a, ctr1, ECaC, esr1) showed principally a down regulation of transcripts with the Cu only treatment, while Ca + Cu treatment restored some of the genes to control levels. Conversely, the Na + Cu treatment had a strong, opposing affect when compared to that of Cu alone. Zebrafish Affymetrix GeneChips revealed significantly clustered patterns of expression. Changes in expression induced by Cu appeared to be opposite to the majority of the other treatments. Our data on the preventative or enhancing effects of Na(+) and Ca(2+) both alone and in the presence of Cu, may, in the future, facilitate the incorporation of gene expression end points into a biotic ligand model predicting chronic Cu toxicity in this tropical model species of genomic importance.
Environmental Science and Technology 02/2010; 44(6):2156-62. · 5.23 Impact Factor
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ABSTRACT: Although copper (Cu) is an essential micronutrient for all organisms, in excess, waterborne Cu poses a significant threat to fish from the cellular to population level. We examined the physiological and gene expression endpoints that chronic waterborne Cu exposure (21 d) imposes on soft-water acclimated zebrafish at two environmentally relevant concentrations: 8 microg/l (moderate) and 15 microg/l (high). Using a 16,730 65-mer oligonucleotide customized zebrafish microarray chip related to metal metabolism and toxicity to assess the transcriptomic response, we found that 573 genes in the liver responded significantly to Cu exposure. These clustered into three distinct patterns of expression. There was distinct upregulation of a majority of these genes under moderate Cu exposure and a significant downregulation under high Cu exposure. Microarray results were validated by qPCR of eight genes; two genes, metallothionein 2 (mt2) and Na(+)-K(+)-ATPase 1a1 (atp1a1), displayed increased expression under both Cu exposures, indicative of potential genetic endpoints of Cu toxicity, whereas the remaining six genes demonstrated opposing effects at each Cu exposure. Na(+)-K(+)-ATPase enzyme activity decreased during Cu exposure, which may be linked to Cu's competitive effects with Na(+). Whole body cortisol levels were significantly increased in Cu-exposed fish, which prompted an analysis of the promoter region of all significantly regulated genes for glucocorticoid (GRE) and metal (MRE) response elements to dissociate metal- and stress-specific gene responses. Of the genes significantly regulated, 30% contained only a GRE sequence, whereas 2.5% contained only a consensus MRE. We conclude that the indirect effects of Cu exposure regulate gene expression to a much greater degree than the direct effects.
Physiological Genomics 09/2009; 40(1):23-33. · 2.73 Impact Factor
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ABSTRACT: Hypoxia (low oxygen) exposure generally leads to decreased reproductive capacity, exhibited by reductions in testicular mass, reproductive hormones, and sperm swimming speed. However, in many fish species, reproduction occurs either periodically or exclusively under hypoxic conditions. In this study we assessed how hypoxia influences sperm per-formance in the plainfin midshipman (Porichthys notatus Girard, 1854), a species that lives in intertidal nests that become hypoxic during low tides. We exposed sperm from the same male to normoxic or hypoxic conditions and compared sperm characteristics and oxygen consumption between treatments. Sperm exposed to hypoxic water swam faster and consumed more oxygen than sperm swimming in normoxic conditions. Sperm swimming speed was positively related with oxygen consumption. For each male, the percentage of motile spermatozoa did not differ between treatments, suggesting that the same number of sperm were active but their performance was dependent on the dissolved oxygen content in the water. We discuss the implications of our results in the context of sperm competition and fertilization success under hypoxic con-ditions. Résumé : Une exposition à l'hypoxie (faibles concentrations d'oxygène) mène généralement à une diminution de la ca-pacité reproductive, ce qui se manifeste par une réduction de la masse testiculaire, des hormones reproductives et de la vi-tesse de nage des spermatozodes. Cependant, chez plusieurs espèces de poissons, la reproduction a lieu périodiquement ou même exclusivement dans des conditions d'hypoxie. Dans notre étude, nous évaluons les influences de l'hypoxie sur la performance des spermatozodes chez le pilotin tacheté (Porichthys notatus Girard, 1854), une espèce qui vit dans des nids intertidaux qui deviennent hypoxiques à marée basse. Nous avons exposé les spermatozodes d'un même mâle à des condi-tions normoxiques ou hypoxiques et avons comparé les caractéristiques des spermatozodes et leur consommation d'oxygène dans les deux conditions expérimentales. Les spermatozodes exposés à l'eau hypoxique nagent plus rapidement et consomment plus d'oxygène que les spermatozodes qui nagent en conditions normoxiques. Il y a une relation positive entre la vitesse de nage des spermatozodes et leur consommation d'oxygène. Chez un même mâle, le pourcentage de sper-matozodes mobiles ne varie pas d'un traitement à l'autre, ce qui laisse croire qu'il y a le même nombre de spermato-zodes en activité, mais que leur performance dépend de la concentration d'oxygène dissous dans l'eau. Nous discutons des implications de nos résultats dans le cadre de la compétition spermatique et du succès de la fécondation dans des con-ditions hypoxiques. [Traduit par la Rédaction]
Canadian Journal of Zoology 01/2009; · 1.21 Impact Factor
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ABSTRACT: Metals like iron (Fe) and copper (Cu) function as integral components in many biological reactions, and, in excess, these essential metals are toxic, and organisms must control metal acquisition and excretion. We examined the effects of chronic waterborne Cu exposure and the interactive effects of elevated dietary Fe on gene expression and tissue metal accumulation in zebrafish. Softwater acclimated zebrafish exposed to 8 microg/l Cu, with and without supplementation of a diet high in Fe (560 vs. 140 mg Fe/kg food) for 21 days demonstrated a significant reduction in liver and gut Cu load relative to waterborne Cu exposure alone. Gene expression levels for divalent metal transport (DMT)-1, copper transporter (CTR)-1, and the basolateral metal transporter ATP7A in the gills and gut increased when compared with controls, but the various combinations of Cu and high-Fe diet revealed altered levels of expression. Further examination of the basolateral Fe transporter, ferroportin, showed responses to waterborne Cu exposure in the gut and a significant increase with Fe treatment alone in the liver. Additionally, we examined metallothionein 1 and 2 (MT1 and MT2), which indicated that MT2 is more responsive to Cu. To explore the relationship between transcription and protein function, we examined both CTR-1 protein levels and gill apical uptake of radiolabeled Cu64, which demonstrated decreased Cu uptake and protein abundance in the elevated Cu treatments. This study shows that high dietary Fe can significantly alter the genetic expression pattern of Cu transporters at the level of the gill, liver, and gastrointestinal tract.
AJP Regulatory Integrative and Comparative Physiology 11/2008; 296(2):R362-73. · 3.34 Impact Factor
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ABSTRACT: Carnitine palmitoyltransferase (CPT) I is regulated by several genetic and non-genetic factors including allosteric inhibition, mitochondrial membrane composition and/or fluidity and transcriptional regulation of enzyme content. To determine the intrinsic differences in these regulating factors that may result in differences between tissues in fatty acid oxidation ability, mitochondria were isolated from red, white and heart muscles and liver tissue from rainbow trout. Maximal activity (V(max)) for beta-oxidation enzymes and citrate synthase per mg tissue protein as well as CPT I in isolated mitochondria followed a pattern across tissues of red muscle>heart>white muscle>liver suggesting both quantitative and qualitative differences in mitochondria. CPT I inhibition showed a similar pattern with the highest malonyl-CoA concentration to inhibit activity by 50% (IC(50)) found in red muscle while liver had the lowest. Tissue malonyl-CoA content was highest in white muscle with no differences between the other tissues. Interestingly, the gene expression profiles did not follow the same pattern as the tissue enzyme activity. CPT I mRNA expression was greatest in heart>red muscle>white muscle>liver. In contrast, PPARalpha mRNA was greatest in the liver>red muscle>heart>white muscle. There were no significant differences in the mRNA expression of PPARbeta between tissues. As well, no significant differences were found in the mitochondrial membrane composition between tissues, however, there was a tendency for red muscle to exhibit higher proportions of PUFAs as well as a decreased PC:PE ratio, both of which would indicate increased membrane fluidity. In fact, there were significant correlations between IC(50) of CPT I for malonyl-CoA and indicators of membrane fluidity across tissues. This supports the notion that sensitivity of CPT I to its allosteric regulator could be modulated by changes in mitochondrial membrane composition and/or fluidity.
Biochimica et Biophysica Acta 06/2008; 1778(6):1382-9. · 4.66 Impact Factor
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ABSTRACT: Idiopathic pulmonary fibrosis (IPF) is a treatment resistant disease with poor prognosis. Numerous compounds have been demonstrated to efficiently prevent pulmonary fibrosis (PF) in animal models but only a few were successful when given to animals with established fibrosis. Major concerns of current PF models are spontaneous resolution and high variability of fibrosis, and the lack of assessment methods that can allow to monitor the effect of drugs in individual animals over time. We used a model of experimental PF in rats and compare parameters obtained in living animals with conventional assessment tools that require removal of the lungs.
PF was induced in rats by adenoviral gene transfer of transforming growth factor-beta. Morphological and functional changes were assessed for up to 56 days by micro-CT, lung compliance (measured via a mechanical ventilator) and VO2max and compared to histomorphometry and hydroxyproline content.
Standard histological and collagen assessment confirmed the persistent fibrotic phenotype as described before. The histomorphological scores correlated both to radiological (r2 = 0.29, p < 0.01) and functional changes (r2 = 0.51, p < 0.0001). VO2max did not correlate with fibrosis.
The progression of pulmonary fibrosis can be reliably assessed and followed in living animals over time using invasive, non-terminal compliance measurements and micro-CT. This approach directly translates to the management of patients with IPF and allows to monitor therapeutic effects in drug intervention studies.
Journal of Translational Medicine 02/2008; 6:16. · 3.41 Impact Factor
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ABSTRACT: In fish, environmental pollution is one factor that induces oxidative stress, and this can disturb the natural antioxidant defense system. Oxidative stress has been well characterized in vitro, yet the in vivo effects of metal-induced oxidative stress have not been extensively studied. In two experiments we examined the impacts of copper (Cu) on gene expression, oxidative damage, and cell oxidative capacity in liver and gill of zebrafish. In the first experiment, soft water-acclimated zebrafish were exposed to 8 and 15 mug/l Cu for 48 h. This exposure resulted in significant increases in gene expression of cytochrome c oxidase subunit 17 (COX-17) and catalase, associated with both increased Cu load and protein carbonyl concentrations in the gill and liver after 48 h. In addition, we examined the potential protective effects of increased waterborne Ca(2+) (3.3 mM) and Na(+) (10 mM) on acute Cu toxicity. While both treatments were effective at reducing liver and/or gill Cu loads and attenuating oxidative damage at 48 h, 10 mM Na(+) was more protective than 3.3 mM Ca(2+). There were variable changes in the maximal activities of COX and citrate synthase (CS), indicating possible alterations in cell oxidative capacity. Moreover, Cu affected COX-to-CS ratios in both gill and liver, suggesting that Cu alters normal mitochondrial biogenic processes, possibly though metallochaperones like COX-17. Overall, this study provides important steps in determining the transcriptional and physiological endpoints of acute Cu toxicity in a model tropical species.
AJP Regulatory Integrative and Comparative Physiology 12/2007; 293(5):R1882-92. · 3.34 Impact Factor
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ABSTRACT: Little is known regarding the ionoregulatory abilities of zebrafish exposed to soft water despite the popularity of this model organism for physiology and aquatic toxicology. We examined genomic and nongenomic changes to gills of zebrafish as they were progressively acclimated from moderately hard freshwater to typical soft water over 7 days and held in soft water for another 7 days. Gills were sampled daily and mRNA expression levels of gill Na(+)-K(+)-ATPase (NKA) alpha1a subunit, epithelium calcium channel (ECaC), carbonic anhydrase-1 and 2 (CA-1, CA-2), Na(+)/H(+) exchanger (NHE-2), V-type proton (H(+))-ATPase, and copper transport protein (CTR-1) were quantified by real-time PCR. Changes in enzyme activities of gill NKA were determined and protein levels of NKA and ECaC were quantified by Western blotting. Levels of mRNA for ECaC increased fourfold after day 6, with an associated increase in ECaC protein levels after 1 wk in soft water. CA-1 and CA-2 exhibited a 1.5- and 6-fold increase in gene expression on days 6 and 5, respectively. Likewise, there was a fivefold increase in NHE-2 expression after day 6. Surprisingly, CTR-1 mRNA showed a large transient increase (over threefold) on day 6, while H(+)-ATPase mRNA did not change. These data demonstrate a high degree of phenotypic plasticity in zebrafish gills exposed to an ion-poor environment. This not only enhances our understanding of ionoregulatory processes in fish but also highlights the need for proper experimental design for studies involving preacclimation to soft water (e.g., metal toxicity).
Physiological Genomics 07/2007; 30(1):53-60. · 2.73 Impact Factor
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ABSTRACT: Both exercise training and cold acclimatization induce muscle remodelling in vertebrates, producing a more aerobic phenotype. In ectothermic species exercise training and cold-acclimatization represent distinct stimuli. It is currently unclear if these stimuli act through a common mechanism or if different mechanisms lead to a common phenotype. The goal of this study was to survey responses that represent potential mechanisms responsible for contraction- and temperature-induced muscle remodelling, using an ectothermic vertebrate. Separate groups of adult zebrafish (Danio rerio) were either swim trained or cold acclimatized for 4 weeks. We found that the mitochondrial marker enzyme citrate synthase (CS) was increased by 1.5x in cold and by 1.3x with exercise (P<0.05). Cytochrome c oxidase (COx) was increased by 1.2x following exercise training (P<0.05) and 1.2x (P=0.07) with cold acclimatization. However, only cold acclimatization increased beta-hydroxyacyl-CoA dehydrogenase (HOAD) compared to exercise-trained (by 1.3x) and pyruvate kinase (PK) relative to control zebrafish. We assessed the whole-animal performance outcomes of these treatments. Maximum absolute sustained swimming speed (Ucrit) was increased in the exercise trained group but not in the cold acclimatized group. Real-time PCR analysis indicated that increases in CS are primarily transcriptionally regulated with exercise but not with cold treatments. Both treatments showed increases in nuclear respiratory factor (NRF)-1 mRNA which was increased by 2.3x in cold-acclimatized and 4x in exercise-trained zebrafish above controls. In contrast, peroxisome proliferator-activated receptor (PPAR)-alpha mRNA levels were decreased in both experimental groups while PPAR-beta1 declined in exercise training only. Moreover, PPAR-gamma coactivator (PGC)-1alpha mRNA was not changed by either treatment. In zebrafish, both temperature and exercise produce a more aerobic phenotype, but there are stimulus-dependent responses (i.e. HOAD and PK activities). While similar changes in NRF-1 mRNA suggest that common responses might underlie aerobic muscle remodelling there are distinct changes (i.e. CS and PPAR-beta1 mRNA) that contribute to specific temperature- and exercise-induced phenotypes.
The Journal of Physiology 12/2006; 577(Pt 2):739-51. · 4.72 Impact Factor
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Grant B McClelland
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ABSTRACT: Lipids are an important fuel for submaximal aerobic exercise. The ways in which lipid oxidation is regulated during locomotion is an area of active investigation. Indeed, the integration between cellular regulation of lipid metabolism and whole-body exercise performance is a fascinating but often overlooked research area. Additionally, the interaction between environmental stress, exercise, and lipid oxidation has not been sufficiently examined. There are many functional and structural steps as fatty acids are mobilized, transported, and oxidized in working muscle, which may serve either as regulatory points for responding to acute or chronic stimuli or as raw material for natural selection. At the whole-animal level, the partitioning of lipids and carbohydrates across exercise intensities is remarkably similar among mammals, which suggests that there is conservation in regulatory mechanisms. Conversely, the proportions of circulatory and intramuscular fuels differ between species and across exercise intensities. Responses to acute and chronic environmental stress likely involve the interaction of genetic and nongenetic changes in the fatty acid pathway. Determining which of these factors help regulate the fatty acid pathway and what impact they have on whole-animal lipid oxidation and performance is an important area of future research. Using an integrative approach to complete the information loop from gene to physiological function provides the most powerful mode of analysis.
Comparative Biochemistry and Physiology Part B Biochemistry and Molecular Biology 12/2004; 139(3):443-60. · 1.92 Impact Factor
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ABSTRACT: Dietary fatty acid composition, particularly polyunsaturated fatty acids, can affect both genetic and non-genetic regulatory mechanisms of carnitine palmitoyltransferase (CPT) I, the main regulatory enzyme of mitochondrial fatty acid oxidation. We aimed to determine how these regulatory mechanisms were affected by changes in the fatty acid composition of the diet in fish. Specifically, we fed rainbow trout (Oncorhynchus mykiss) either a high polyunsaturated fatty acid (PUFA) diet, a high saturated fatty acid (SFA) diet or a mixed fatty acid control (CTL) diet for 8 weeks to determine if modifications of the dietary fatty acids would affect 1) the genetic expression of CPT I and its transcription factor peroxisome proliferator activated receptor (PPAR), 2) the mitochondrial membrane composition and if these modifications would affect CPT I sensitivity to malonyl-CoA, and 3) levels of malonyl-CoA in the tissues. We found that fish fed the high PUFA diet significantly increased CPT I mRNA expression in red muscle, liver and adipose tissue, while PPAR α and β expressions were variable across tissues. Few significant changes were observed in the mitochondrial membrane composition with the exception of DHA in the red muscle. There were no significant differences in CPT I sensitivity to malonyl-CoA or the malonyl-CoA content of the tissues with either experimental diet. Our present data suggest that changes in gene expression of CPT I and PPARs is the main regulatory mechanism controlling CPT I function in fish using our experimental diet.
Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology.
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ABSTRACT: Dogfish sharks are opportunistic predators, eating large meals at irregular intervals. Here we present a synthesis of data from several previous studies on responses in plasma metabolites after natural feeding and during prolonged fasting (up to 56 days), together with new data on changes in plasma concentrations of amino acids and non-esterified fatty acids. Post-prandial and long-term fasting responses were compared to control sharks fasted for 7 days, a typical inter-meal interval. A feeding frenzy was created in which dogfish were allowed to feed naturally on dead teleosts at two consumed ration levels, 2.6% and 5.5% of body weight. Most responses were more pronounced at the higher ration level. These included increases in urea and TMAO concentrations at 20 h, followed by stability through to 56 days of fasting. Ammonia levels were low and exhibited little short-term response to feeding, but declined to very low values during the extended fast. Glucose and β-hydroxybutyrate both fell after feeding, the latter to a greater and more prolonged extent (up to 60 h), whereas acetoacetate did not change. During prolonged fasting, glucose concentrations were well regulated, but β-hydroxybutyrate increased to 2–3-fold control levels. Total plasma amino acid concentrations increased in a biphasic fashion, with peaks at 6–20 h, and 48–60 h after the meal, followed by homeostasis during the extended fast. Essential and non-essential amino acids generally followed this same pattern, though some exhibited different trends after feeding: taurine, β-alanine, and glycine (decreases or stability), alanine and glutamine (modest prolonged increases), and threonine, serine, asparagine, and valine (much larger short-term increases). Plasma non-esterified fatty acid concentrations declined markedly through 48 h after the 2.6% meal. These data are interpreted in light of companion studies showing elevations in aerobic metabolic rate, urea production, rectal gland function, metabolic base excretion, and activation of ornithine–urea cycle and aerobic enzymes after the meal, and muscle N-depletion but maintenance of osmolality and urea production during long-term fasting.
Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology.
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ABSTRACT: Periods of fasting, in most animals, are fueled principally by fatty acids, and changes in the regulation of fatty acid oxidation must exist to meet this change in metabolic substrate use. We examined the regulation of carnitine palmitoyltransferase (CPT) I, to help explain changes in mitochondrial fatty acid oxidation with fasting. After fasting rainbow trout (Oncorhynchus mykiss) for 5 wk, the mitochondria were isolated from red muscle and liver to determine (1) mitochondrial fatty acid oxidation rate, (2) CPT I activity and the concentration of malonyl-CoA needed to inhibit this activity by 50% (IC(50)), (3) mitochondrial membrane fluidity, and (4) CPT I (all five known isoforms) and peroxisome proliferator-activated receptor (PPARα and PPARβ) mRNA levels. Fatty acid oxidation in isolated mitochondria increased during fasting by 2.5- and 1.75-fold in liver and red muscle, respectively. Fasting also decreased sensitivity of CPT I to malonyl-CoA (increased IC(50)), by two and eight times in red muscle and liver, respectively, suggesting it facilitates the rate of fatty acid oxidation. In the liver, there was also a significant increase CPT I activity per milligram mitochondrial protein and in whole-tissue PPARα and PPARβ mRNA levels. However, there were no changes in mitochondrial membrane fluidity in either tissue, indicating that the decrease in CPT I sensitivity to malonyl-CoA is not due to bulk fluidity changes in the membrane. However, there were significant differences in CPT I mRNA levels during fasting. Overall, these data indicate some important changes in the regulation of CPT I that promote the increased mitochondrial fatty acid oxidation that occurs during fasting in trout.
Physiological and Biochemical Zoology 84(6):625-33. · 2.20 Impact Factor
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ABSTRACT: BackgroundIn mammals, environmental challenges often result in physical and metabolic cardiac remodeling (i.e., hypertrophy and a shift from lipid to carbohydrate oxidation). While chronic hypoxia and cold are both known to elicit cardiac changes, little is known about their combined effects.MethodsTo investigate the cumulated effects of these two stressors on cardiac physiology, CD-1 mice were exposed for 4 weeks to normoxia/normothermia, hypoxia, cold, or combined hypoxic–cold. We assessed physical characteristics, left ventricular activities of fatty acid catabolic enzymes short-chain β-hydroxyacyl-CoA dehydrogenase (SCHAD) and medium-chain acyl-CoA dehydrogenase, and mRNA levels of Acadm, muscle- and liver-type carnitine palmitoyltransferase (Cpt-1β, Cpt-1α), and the transcriptional regulator PPARα.Results1) Chronic hypoxia reduced SCHAD activity without physical remodeling or mRNA changes; 2) chronic cold lead to reduced SCHAD activity in hypertrophied left ventricles and lowered right ventricular Cpt-1α mRNA (compared to chronic hypoxia); and 3) despite causing hypertrophy of both ventricles, chronic exposure to combined hypoxic–cold did not induce significant metabolic remodeling.General SignificanceIn response to environmental challenges, cardiac muscles 1) show distinct physical and metabolic remodeling, 2) respond to two stressors simultaneously but not additively, and 3) maintain an adult metabolic phenotype with long-term exposure to environmentally realistic hypoxic–cold.
Biochimica et Biophysica Acta (BBA) - General Subjects.
