Papers by Daniel Kostyniuk
Rainbow trout are an important salmonid species whose poor utilization of dietary carbohydrates s... more Rainbow trout are an important salmonid species whose poor utilization of dietary carbohydrates spurred research investigating molecular and physiological components of its glucoregulation. Among the environmental factors described to exert robust changes in glucose metabolism in rainbow trout, nutrition and social stress are among the most studied: Diets To begin I would like to express my sincerest gratitude to my supervisor, Dr. Jan Mennigen, for his enthusiasm, guidance and support throughout the course of my Master's. His positivity, patience and energy propelled me through this project. He helped me develop a greater understanding and appreciation for research and science, and I am grateful to him for this opportunity and am proud of the research we have published together. Second, I would like to thank my committee members, Dr. Kathleen Gilmour, Dr. Tom Moon and Dr. Ken Storey, for their time, feedback and comments on my project. I am fortunate to have been able to work with such knowledgeable scientists. Additionally, I am extremely grateful for my experience at INRA in Saint-Pée-sur-Nivelle in France under the supervision of Dr. Lucie Marandel and Vincent Veron. I learned valuable lessons in trouble shooting and the experiences and connections I made are invaluable. Thanks also to Jingwei Liu for helping me get to know the other students and researchers so I had people to eat lunch with. I would also like to extend my thanks to the Mennigen and Gilmour labs. Your support the past three years collectively has been amazing, and I am lucky to be a part and collaborate with a great group of people. A special thank you to Carol Best for her v help all the way back to when I was doing my coop and honours project, Jon Tea for also working at the lab at ridiculous hours of the night, Mais Jubouri for helping kickstart the Mennigen lab and everyone else who has helped along the way. To all those that I have been fortunate enough to collaborate with over my time at UOttawa who have not already been mentioned, Rubén Francisco Martínez López, Johnathon Forbes, Elie Farhat, and Dr. Wenqing Tu, you all made coming into the lab enjoyable and interesting. Additionally, I am very appreciative of Bill Fletcher, Christine Archer and ACVS for their help with animal care, answering my questions and making it possible to run the experiments. To my family and friends, for all your support and understanding of my long days, late nights and all-nighters when the qPCR machine was available. Especially my parents Tim and Ambra Kostyniuk who supported me throughout and picked me up from the bus stop many times late at night; and my sisters Anna and Laura Kostyniuk for being my confidants and making me laugh in my times of struggle while being the greatest hypewomen when things were going well, thank you. Finally, thank you Sarah Best for your support and understanding throughout this process, it's been a long one. vi
Rainbow trout are an important salmonid species whose poor utilization of dietary carbohydrates s... more Rainbow trout are an important salmonid species whose poor utilization of dietary carbohydrates spurred research investigating molecular and physiological components of its glucoregulation. Among the environmental factors described to exert robust changes in glucose metabolism in rainbow trout, nutrition and social stress are among the most studied: Diets To begin I would like to express my sincerest gratitude to my supervisor, Dr. Jan Mennigen, for his enthusiasm, guidance and support throughout the course of my Master's. His positivity, patience and energy propelled me through this project. He helped me develop a greater understanding and appreciation for research and science, and I am grateful to him for this opportunity and am proud of the research we have published together. Second, I would like to thank my committee members, Dr. Kathleen Gilmour, Dr. Tom Moon and Dr. Ken Storey, for their time, feedback and comments on my project. I am fortunate to have been able to work with such knowledgeable scientists. Additionally, I am extremely grateful for my experience at INRA in Saint-Pée-sur-Nivelle in France under the supervision of Dr. Lucie Marandel and Vincent Veron. I learned valuable lessons in trouble shooting and the experiences and connections I made are invaluable. Thanks also to Jingwei Liu for helping me get to know the other students and researchers so I had people to eat lunch with. I would also like to extend my thanks to the Mennigen and Gilmour labs. Your support the past three years collectively has been amazing, and I am lucky to be a part and collaborate with a great group of people. A special thank you to Carol Best for her v help all the way back to when I was doing my coop and honours project, Jon Tea for also working at the lab at ridiculous hours of the night, Mais Jubouri for helping kickstart the Mennigen lab and everyone else who has helped along the way. To all those that I have been fortunate enough to collaborate with over my time at UOttawa who have not already been mentioned, Rubén Francisco Martínez López, Johnathon Forbes, Elie Farhat, and Dr. Wenqing Tu, you all made coming into the lab enjoyable and interesting. Additionally, I am very appreciative of Bill Fletcher, Christine Archer and ACVS for their help with animal care, answering my questions and making it possible to run the experiments. To my family and friends, for all your support and understanding of my long days, late nights and all-nighters when the qPCR machine was available. Especially my parents Tim and Ambra Kostyniuk who supported me throughout and picked me up from the bus stop many times late at night; and my sisters Anna and Laura Kostyniuk for being my confidants and making me laugh in my times of struggle while being the greatest hypewomen when things were going well, thank you. Finally, thank you Sarah Best for your support and understanding throughout this process, it's been a long one. vi
Meta-analysis of differentially-regulated hepatic microRNAs identifies candidate post-transcriptional regulation networks of intermediary metabolism in rainbow trout
Comparative Biochemistry and Physiology Part D: Genomics and Proteomics
Meta-analysis of differentially-regulated hepatic microRNAs identifies candidate post-transcriptional regulation networks of intermediary metabolism in rainbow trout
Comparative Biochemistry and Physiology Part D: Genomics and Proteomics, Dec 1, 2020
MicroRNAs (miRNAs) are small non-coding RNAs which act as post-transcriptional regulators by decr... more MicroRNAs (miRNAs) are small non-coding RNAs which act as post-transcriptional regulators by decreasing targeted mRNA translation and stability. Principally targeting small 3' UTR elements of protein-coding mRNAs through complementary base-pairing, miRNAs are promiscuous regulators of the transcriptome. While potent roles for hepatic miRNAs in the regulation of energy metabolism have emerged in rodent models, comparative roles in other vertebrates remain largely unexplored. Indeed, while several miRNAs are deeply conserved among vertebrates, the acquisition of lineage- and species-specific miRNAs, as well as the rewiring between miRNA-mRNA target relationships beg the question of regulatory and functional conservation and innovation of miRNAs and their targets involved in energy metabolism. Here we provide a meta-analysis of differentially expressed hepatic miRNAs in rainbow trout, a scientifically and economically important teleost species with a 'glucose-intolerant' phenotype. Following exposure to nutritional and social context-dependent metabolic challenges, we analyzed differential miRNA expression from small-RNA-sequencing datasets generated with a consistent bioinformatics pipeline in conjunction with an in silico target prediction of metabolic transcripts and pathways. We provide evidence for evolutionary conserved (let-7, miRNA-27 family) and rewired (miRNA-30 family, miRNA-152, miRNA-722) miRNA-metabolic target gene networks in the context of the salmonid genome. These findings represent important first steps in our understanding of the comparative regulation and function of hepatic miRNAs in rainbow trout energy metabolism. We propose that the identified miRNA families should be prioritized for future comparative functional investigation in the context of hepatic energy- and glucose metabolism in rainbow trout.
Journal of Comparative Physiology B-biochemical Systemic and Environmental Physiology, Mar 12, 2021
When confined in pairs, juvenile rainbow trout (Oncorhynchus mykiss) form dominance hierarchies i... more When confined in pairs, juvenile rainbow trout (Oncorhynchus mykiss) form dominance hierarchies in which subordinate fish exhibit characteristic physiological changes including reduced growth rates and chronically elevated plasma cortisol concentrations. We hypothesized that alterations in protein metabolism contribute to the reduced growth rate of socially stressed trout, and predicted that subordinate trout would exhibit reduced rates of protein synthesis coupled with increases in protein degradation. Protein metabolism was assessed in dominant and subordinate fish after 4 days of social interaction, and in fish that were separated after 4 days of interaction for a 4 days recovery period, to determine whether effects on protein metabolism recovered when social stress was alleviated. Protein metabolism was assessed in liver and white muscle by measuring the fractional rate of protein synthesis and markers of protein degradation. In the white muscle of subordinate fish, protein synthesis was inhibited and activities of the ubiquitin-proteasome pathway (UPP) and the autophagy lysosomal system (ALS) were elevated. By contrast, the liver of subordinate fish exhibited increased rates of protein synthesis and activation of the ALS. When allowed to recover from chronic social stress for 4 days, differences in protein metabolism observed in white muscle of subordinate fish during the interaction period disappeared. In liver, protein synthesis returned to baseline levels during recovery from social stress, but markers of protein degradation did not. Collectively, these data support the hypothesis that inhibition of muscle protein synthesis coupled with increases in muscle protein breakdown contribute to the reduced growth rates of subordinate rainbow trout.
Journal of Comparative Physiology B, 2021
When confined in pairs, juvenile rainbow trout (Oncorhynchus mykiss) form dominance hierarchies i... more When confined in pairs, juvenile rainbow trout (Oncorhynchus mykiss) form dominance hierarchies in which subordinate fish exhibit characteristic physiological changes including reduced growth rates and chronically elevated plasma cortisol concentrations. We hypothesized that alterations in protein metabolism contribute to the reduced growth rate of socially stressed trout, and predicted that subordinate trout would exhibit reduced rates of protein synthesis coupled with increases in protein degradation. Protein metabolism was assessed in dominant and subordinate fish after 4 days of social interaction, and in fish that were separated after 4 days of interaction for a 4 days recovery period, to determine whether effects on protein metabolism recovered when social stress was alleviated. Protein metabolism was assessed in liver and white muscle by measuring the fractional rate of protein synthesis and markers of protein degradation. In the white muscle of subordinate fish, protein synt...
Supplemental Data 4.xlsx
supplemental figures for doi:10.1152/physiological genomics.00001.2020
Suppl. Data 2.xlsx
supplemental figures for doi:10.1152/physiological genomics.00001.2020
Physiological Genomics, 2020
Elucidating molecular pathways regulating neuroimmune communication is critical for therapeutic i... more Elucidating molecular pathways regulating neuroimmune communication is critical for therapeutic interventions in conditions characterized by overactive immune responses and dysfunctional autonomic nervous system. We generated a bone marrow-specific adrenergic beta 1 and beta 2 knockout mouse chimera (AdrB1.B2 KO) to determine how sympathetic drive to the bone affects transcripts and miRNAs in the hypothalamic paraventricular nucleus (PVN). This model has previously exhibited a dampened systemic immune response and decreased blood pressure compared with control animals. Reduced sympathetic responsiveness of the bone marrow hematopoietic cells of AdrB1.B2 KO chimera led to suppression of transcriptional networks that included leukocyte cell adhesion and migration and T cell-activation and recruitment. Transcriptome responses related to IL-17a signaling and the renin-angiotensin system were also suppressed in the PVN. Based on the transcriptome response, we next computationally predict...
Physiological Genomics, 2020
Elucidating molecular pathways regulating neuroimmune communication is critical for therapeutic i... more Elucidating molecular pathways regulating neuroimmune communication is critical for therapeutic interventions in conditions characterized by overactive immune responses and dysfunctional autonomic nervous system. We generated a bone marrow-specific adrenergic beta 1 and beta 2 knockout mouse chimera (AdrB1.B2 KO) to determine how sympathetic drive to the bone affects transcripts and miRNAs in the hypothalamic paraventricular nucleus (PVN). This model has previously exhibited a dampened systemic immune response and decreased blood pressure compared with control animals. Reduced sympathetic responsiveness of the bone marrow hematopoietic cells of AdrB1.B2 KO chimera led to suppression of transcriptional networks that included leukocyte cell adhesion and migration and T cell-activation and recruitment. Transcriptome responses related to IL-17a signaling and the renin-angiotensin system were also suppressed in the PVN. Based on the transcriptome response, we next computationally predicted miRNAs in the PVN that may underscore the reduced sympathetic responsiveness of the bone marrow cells. These included miR-27b-3p, miR-150, miR-223-3p, and miR-326. Using real-time PCR, we measured a downregulation in the expression of miR-150-5p, miR-205-5p, miR-223-3p, miR-375-5p, miR-499a-5p, miR-27b-3p, let-7a-5p, and miR-21a-5p in the PVN of AdrB1.B2 KO chimera, confirming computational predictions that these miRNAs are associated with reduced neuro-immune responses and the loss of sympathetic responsiveness in the bone marrow. Intriguingly, directional responses of the miRNA corresponded to mRNAs, suggesting complex temporal or circuit-dependent posttranscriptional control of gene expression in the PVN. This study identifies molecular pathways involved in neural-immune interactions that may act as targets of therapeutic intervention for a dysfunctional autonomic nervous system.
Journal of Experimental Biology, 2019
Glucagon increases fish glycemia, but how it affects glucose fluxes in vivo has never been charac... more Glucagon increases fish glycemia, but how it affects glucose fluxes in vivo has never been characterized. The goal of this study was to test the hypothesis that glucagon stimulates hepatic glucose production (Ra) and inhibits disposal (Rd) of rainbow trout. Changes in the mRNA abundance of key proteins involved in glycolysis, gluconeogenesis, and glycogen breakdown were also monitored. Results show that glucagon increases glycemia (+38%) by causing a temporary mismatch between Ra and Rd before both fluxes converge below baseline (-17%). A novel aspect of the regulation of trout gluconeogenesis is also demonstrated: the completely different effects of glucagon on the expression of three Pepck isoforms (stimulation of pck1, inhibition of pck2a, and no response of pck2b). Glycogen phosphorylase was modulated differently among tissues, and muscle upregulated pygb and downregulated pygm. Glucagon failed to activate the cAMP-dependent protein kinase or FoxO1 signalling cascades. We conclu...
Environmental Science & Technology, 2019
Environmental Science & Technology, 2019
The novel PFOS alternatives, 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p... more The novel PFOS alternatives, 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) and sodium p-perfluorous nonenoxybenzenesulfonate (OBS), are emerging in the Chinese market, but little is known about their ecological risks. In this study, zebrafish embryos were exposed to PFOS, F-53B, and OBS to evaluate their bioconcentration and acute metabolic consequences. Per- and polyfluoroalkyl substances (PFASs) accumulated in larvae in the order of F-53B > PFOS > OBS, with the bioconcentration factors ranging from 20 to 357. Exposure to F-53B and PFOS, but not OBS, increased energy expenditure, and reduced feed intake in a concentration-dependent manner and the expression of genes involved in metabolic pathways at the transcriptional and translational levels. Molecular docking revealed that the binding affinities of PFASs to glucokinase were decreased in the following order: F-53B > PFOS > OBS. Finally, the results of Point of Departure (PoD) indicate that metabolic end points at the molecular and organismal level are most sensitive to F-53B followed by PFOS and OBS. Collectively, F-53B has the highest bioconcentration potential and the strongest metabolism-disrupting effects, followed by PFOS and OBS. Our findings have important implications for the assessment of early developmental metabolic effects of PFOS alternatives F-53B and OBS in wildlife and humans.
Physiological Genomics, 2019
Carnivorous rainbow trout exhibit prolonged postprandial hyperglycemia when fed a diet exceeding ... more Carnivorous rainbow trout exhibit prolonged postprandial hyperglycemia when fed a diet exceeding 20% carbohydrate content. This poor capacity to utilize carbohydrates has led to rainbow trout being classified as “glucose-intolerant” (GI). The metabolic phenotype has spurred research to identify the underlying cellular and molecular mechanisms of glucose intolerance, largely because carbohydrate-rich diets provide economic and ecological advantages over traditionally used fish meal, considered unsustainable for rainbow trout aquaculture operations. Evidence points to a contribution of hepatic intermediary carbohydrate and lipid metabolism, as well as upstream insulin signaling. Recently, microRNAs (miRNAs), small noncoding RNAs acting as negative posttranscriptional regulators affecting target mRNA stability and translation, have emerged as critical regulators of hepatic control of glucose-homeostasis in mammals, revealing that dysregulated hepatic miRNAs might play a role in organis...
Profiling the rainbow trout hepatic miRNAome under diet-induced hyperglycemia, 2019
Profiling the rainbow trout hepatic miRNAome under diet-induced hyperglycemia.Carnivorous rainbow... more Profiling the rainbow trout hepatic miRNAome under diet-induced hyperglycemia.Carnivorous rainbow trout exhibit prolonged postprandial hyperglycemia when fed a diet exceeding 20% carbohydrate content. This poor capacity to utilize carbohydrates has led to rainbow trout being classified as "glucose-intolerant" (GI). The metabolic phenotype has spurred research to identify the underlying cellular and molecular mechanisms of glucose intolerance, largely because carbohydrate-rich diets provide economic and ecological advantages over traditionally used fish meal, considered un-sustainable for rainbow trout aquaculture operations. Evidence points to a contribution of hepatic intermediary carbohydrate and lipid metabolism, as well as upstream insulin signaling. Recently, microRNAs (miRNAs), small noncoding RNAs acting as negative posttranscrip-tional regulators affecting target mRNA stability and translation, have emerged as critical regulators of hepatic control of glucose-homeo-stasis in mammals, revealing that dysregulated hepatic miRNAs might play a role in organismal hyperglycemia in metabolic disease. To determine whether hepatic regulatory miRNA networks may contribute to GI in rainbow trout, we induced prolonged postprandial hyper-glycemia in rainbow trout by using a carbohydrate-rich diet and profiled genome-wide hepatic miRNAs in hyperglycemic rainbow trout compared with fasted trout and trout fed a diet devoid of carbohydrates. Using small RNA next-generation sequencing and real-time RT-PCR validation, we identified differentially regulated hepatic miRNAs between these groups and used an in silico approach to predict bona fide mRNA targets and enriched pathways. Diet-induced hyperglycemia resulted in differential regulation of hepatic miRNAs compared with fasted fish. Some of the identified miRNAs, such as miRNA-27b-3p and miRNA-200a-3p, are known to be responsive to hyperglycemia in the liver of hyperglycemic glucose-tolerant fish and mammals, suggesting an evolutionary conserved regulation. Using Gene Ontology term-based enrichment analysis, we identify intermediate carbohydrate and lipid metabolism and insulin signaling as potential targets of posttranscriptional regulation by hyperglyce-mia-regulated miRNAs and provide correlative expression analysis of specific predicted miRNA-target pairs. This study identifies hepatic miRNAs in rainbow trout that exhibit differential postprandial expression in response to diets with different carbohydrate content and predicts posttranscriptionally regulated target mRNAs enriched for pathways involved in glucoregulation. Together, these results provide a framework for testable hypotheses of functional involvement of specific hepatic miRNAs in GI in rainbow trout.
Gene, 2019
Rainbow trout have, as salmonid fish species, undergone sequential genome duplication events in t... more Rainbow trout have, as salmonid fish species, undergone sequential genome duplication events in their evolutionary history. In addition to a teleost-specific whole genome duplication approximately 320-350 million years ago, rainbow trout and salmonids in general underwent an additional salmonid lineage-specific genome duplication event approximately 80 million years ago. Through the recent sequencing of salmonid genome sequences, including the rainbow trout, the identification and study of duplicated genes has become available. A particular focus of interest has been the evolution and regulation of rainbow trout gluconeogenic genes, as recent molecular and gene expression evidence points to a possible contribution of previously uncharacterized gluconeogenic gene paralogues to the rainbow trout long-studied glucose intolerant phenotype. Since the publication of the initial rainbow trout genome draft, resequencing and annotation have further improved genome coverage. Taking advantage of these recent improvements, we here identify a salmonid-specific genome duplication of ancestral mitochondrial phosphoenolpyruvate carboxykinase 2 isoenzyme, we termed pck2a and pck2b. Cytosolic phosphoenolpyruvate carboxykinase (Pck1) and, more recently mitochondrial Pck2, are considered to be the rate-limiting enzymes in de novo gluconeogenesis. Following in silico confirmation of salmonid pck2a and pck2b evolutionary history, we simultaneously profiled cytosolic pck1 and mitochondrial pck2a and pck2b expression in rainbow trout liver under several experimental conditions known to regulate hepatic gluconeogenesis. Cytosolic pck1 abundance was increased by nutritional (diets with a high protein to carbohydrate ratio compared to diets with a low carbohydrate to protein ratio) and glucoregulatory endocrine factors (glucagon and cortisol), revealing that the well-described transcriptional regulation of pck1 in mammals is present in rainbow trout. Conversely, and in contrast to mammals, we here describe endocrine regulation of pck2a (decrease in abundance in response to glucagon infusion), and nutritional, social-status-dependent and hypoxiadependent regulation of pck2b. Specifically, pck2b transcript abundance increased in trout fed a diet with a low protein to carbohydrate ratio compared to a diet with a high protein to carbohydrate ratio, in dominant fish compared to subordinate fish as well as hypoxia. This specific and differential expression of rainbow trout pck2 ohnologues is indicative of functional diversification, and possible functional consequences are discussed in light of the recently highlighted gluconeogenic roles of mitochondrial pck2 in mammalian models.
Pck-ing up steam: Widening the salmonid gluconeogenic gene duplication trail, 2019
Rainbow trout have, as salmonid fish species, undergone sequential genome duplication events in t... more Rainbow trout have, as salmonid fish species, undergone sequential genome duplication events in their evolutionary history. In addition to a teleost-specific whole genome duplication approximately 320-350 million years ago, rainbow trout and salmonids in general underwent an additional salmonid lineage-specific genome duplication event approximately 80 million years ago. Through the recent sequencing of salmonid genome sequences , including the rainbow trout, the identification and study of duplicated genes has become available. A particular focus of interest has been the evolution and regulation of rainbow trout gluconeogenic genes, as recent molecular and gene expression evidence points to a possible contribution of previously uncharacterized glu-coneogenic gene paralogues to the rainbow trout long-studied glucose intolerant phenotype. Since the publication of the initial rainbow trout genome draft, resequencing and annotation have further improved genome coverage. Taking advantage of these recent improvements, we here identify a salmonid-specific genome duplication of ancestral mitochondrial phosphoenolpyruvate carboxykinase 2 isoenzyme, we termed pck2a and pck2b. Cytosolic phosphoenolpyruvate carboxykinase (Pck1) and, more recently mitochondrial Pck2, are considered to be the rate-limiting enzymes in de novo gluconeogenesis. Following in silico confirmation of salmonid pck2a and pck2b evolutionary history, we simultaneously profiled cytosolic pck1 and mitochondrial pck2a and pck2b expression in rainbow trout liver under several experimental conditions known to regulate hepatic glu-coneogenesis. Cytosolic pck1 abundance was increased by nutritional (diets with a high protein to carbohydrate ratio compared to diets with a low carbohydrate to protein ratio) and glucoregulatory endocrine factors (glu-cagon and cortisol), revealing that the well-described transcriptional regulation of pck1 in mammals is present in rainbow trout. Conversely, and in contrast to mammals, we here describe endocrine regulation of pck2a (de-crease in abundance in response to glucagon infusion), and nutritional, social-status-dependent and hypoxia-dependent regulation of pck2b. Specifically, pck2b transcript abundance increased in trout fed a diet with a low protein to carbohydrate ratio compared to a diet with a high protein to carbohydrate ratio, in dominant fish compared to subordinate fish as well as hypoxia. This specific and differential expression of rainbow trout pck2 ohnologues is indicative of functional diversification, and possible functional consequences are discussed in light of the recently highlighted gluconeogenic roles of mitochondrial pck2 in mammalian models.
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2018
Juvenile rainbow trout ( Oncorhynchus mykiss) confined in pairs form social hierarchies in which ... more Juvenile rainbow trout ( Oncorhynchus mykiss) confined in pairs form social hierarchies in which socially subordinate fish display characteristic traits, including reduced growth rates and altered glucose metabolism. These effects are, in part, mediated by chronically elevated cortisol levels and/or reduced feeding. To determine the effects of social status on lipid metabolism, trout were held in pairs for 4 days, following which organismal and liver-specific indexes of lipid metabolism were measured. At the organismal level, circulating triglycerides were elevated in dominant trout, whereas subordinate trout exhibited elevated concentrations of circulating free fatty acids (FFAs) and lowered plasma total cholesterol levels. At the molecular level, increased expression of lipogenic genes in dominant trout and cpt1a in subordinate trout was identified, suggesting a contribution of increased de novo lipogenesis to circulating triglycerides in dominant trout and reliance on circulating...
Social status affects lipid metabolism in rainbow trout, Oncorhynchus mykiss, 2018
Juvenile rainbow trout (Oncorhynchus mykiss) confined in pairs form social hierarchies in which s... more Juvenile rainbow trout (Oncorhynchus mykiss) confined in pairs form social hierarchies in which socially subordinate fish display characteristic traits, including reduced growth rates and altered glucose metabolism. These effects are, in part, mediated by chronically elevated cortisol levels and/or reduced feeding. To determine the effects of social status on lipid metabolism, trout were held in pairs for 4 days, following which organ-ismal and liver-specific indexes of lipid metabolism were measured. At the organismal level, circulating triglycerides were elevated in dominant trout, whereas subordinate trout exhibited elevated concentrations of circulating free fatty acids (FFAs) and lowered plasma total cholesterol levels. At the molecular level, increased expression of lipogenic genes in dominant trout and cpt1a in subordinate trout was identified, suggesting a contribution of increased de novo lipogenesis to circulating triglycerides in dominant trout and reliance on circulating FFAs for-oxidation in the liver of subordinates. Given the emerging importance of microRNAs (miRNA) in the regulation of hepatic lipid metabolism, candidate miRNAs were profiled, revealing increased expression of the lipogenic miRNA-33 in dominant fish. Because the Akt-TOR-S6-signaling pathway is an important upstream regulator of hepatic lipid metabolism, its signaling activity was quantified. However, the only difference detected among groups was a strong increase in S6 phosphorylation in subordinate trout. In general, the changes observed in lipid metabolism of subordinates were not mimicked by either cortisol treatment or fasting alone, indicating the existence of specific, emergent effects of subordinate social status itself on this fuel.
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 2019
The physiological reasons why salmonids show glucose intolerance are unclear. In mammals, rapid c... more The physiological reasons why salmonids show glucose intolerance are unclear. In mammals, rapid clearance of a glucose load is mainly achieved through insulin-mediated inhibition of hepatic glucose production ( Ra) and stimulation of glucose disposal ( Rd), but the effects of insulin on Raand Rdglucose have never been measured in fish. The goal of this study was to characterize the impact of insulin on the glucose kinetics of rainbow trout in vivo. Glucose fluxes were measured by continuous infusion of [6-3H]glucose before and during 4 h of insulin administration. The phosphorylated form of the key signaling proteins Akt and S6 in the insulin cascade were also examined, confirming activation of this pathway in muscle but not liver. Results show that insulin inhibits trout Rdglucose from 8.6 ± 0.6 to 5.4 ± 0.5 µmol kg−1min−1: the opposite effect than classically seen in mammals. Such a different response may be explained by the contrasting effects of insulin on gluco/hexokinases of t...
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Papers by Daniel Kostyniuk