Role of the PGC-1 family in the metabolic adaptation of goldfish to diet and temperature

Daily thermal variability does not modify long-term gene expression relative to stable thermal environments: A case study of a tropical fish

Global warming is leading to an increase in the frequency and intensity of extreme weather events, magnifying the breadth of temperatures faced by ectotherms across days and seasons. Despite the importance and ecological relevance of diurnal thermal variability, the vast majority of knowledge on gene expression patterns and physiology stems from animals acclimated to constant temperatures or in the early stages of exposure to a new temperature regime. If heterothermal environments modulate responses differently from constant thermal environments, our existing capacity to forecast impacts of climate warming may be compromised. To address this knowledge gap, we acclimated barramundi (Lates calcarifer) to 23 °C, 29 °C (optimal), 35 °C and to thermal cycling conditions (23-35 °C daily with a mean of 29 °C) and sampled liver and white muscle tissue before acclimation and after 2 and 17 weeks of acclimation. NanoString nCounter technologies were used to measure expression of 20 genes related to metabolism, growth and maintenance of cellular homeostasis. Acclimation to cool and warm conditions caused predictable changes in whole-animal performance (metabolism and growth) and the underlying gene expression patterns. Acclimation to a cycling temperature regime did not change the molecular regulation of metabolism or growth compared with barramundi acclimated to constant 29 °C, nor did it cause any discernible effects on whole-animal performance. However, the heat shock response was higher in the former group, suggesting that barramundi under a daily temperature cycle have an increased need for cellular chaperoning to minimise detrimental effects of temperature on proteins. We conclude that the genetic regulation of metabolism and growth may be more dependent on the mean daily temperature than on the daily temperature range.

Muscle Transcriptome Sequencing Revealed Thermal Stress-Responsive Regulatory Genes in Farmed Rohu, Labeo rohita (Hamilton, 1822)

Rohu, Labeo rohita, is one of the most important aquaculture species in the Indian subcontinent. Understanding the molecular-level physiological responses to thermal stress or climate change is essential. In the present work, transcriptome sequencing was carried out in the muscle tissue of the rohu in response to heat stress (35 °C) in comparison with the control (28 °C). A total of 125 Gb of sequence data was generated, and the raw-reads were filtered and trimmed, which resulted in 484 million quality reads. Reference-based assembly of reads was performed using L. rohita genome, and a total of 90.17% of reads were successfully mapped. A total of 37,462 contigs were assembled with an N50 value of 1854. The differential expression analysis revealed a total of 107 differentially expressed genes (DEGs) (15 up-, 37 down-, and 55 neutrally regulated) as compared to the control group (Log2FC > 2, P < 0.05). Gene enrichment analysis of DEGs indicates that transcripts were associated with molecular, biological, and cellular activities. The randomly selected differentially expressed transcripts were validated by RT-qPCR and found consistent expression patterns in line with the RNA-seq data. Several transcripts such as SERPINE1(HSP47), HSP70, HSP90alpha, Rano class II histocompatibility A beta, PGC-1 and ERR-induced regulator, proto-oncogene c-Fos, myozenin2, alpha-crystallin B chain-like protein, angiopoietin-like protein 8, and acetyl-CoA carboxylases have been identified in muscle tissue of rohu that are associated with stress/immunity. This study identified the key biomarker SERPINE1 (HSP47), which showed significant upregulation (~ 2- to threefold) in muscle tissue of rohu exposed to high temperature. This study can pave a path for the identification of stress-responsive biomarkers linked with thermal adaptations in the farmed carps.

Regulation of PGC-1α of the Mitochondrial Energy Metabolism Pathway in the Gills of Indian Medaka (Oryzias dancena) under Hypothermal Stress

Ectothermic fish exposure to hypothermal stress requires adjusting their metabolic molecular machinery, which was investigated using Indian medaka (Oryzias dancena; 10 weeks old, 2.5 ± 0.5 cm) cultured in fresh water (FW) and seawater (SW; 35‱) at room temperature (28 ± 1 °C). The fish were fed twice a day, once in the morning and once in the evening, and the photoperiod was 12 h:12 h light: dark. In this study, we applied two hypothermal treatments to reveal the mechanisms of energy metabolism via pgc-1α regulation in the gills of Indian medaka; cold-stress (18 °C) and cold-tolerance (extreme cold; 15 °C). The branchial ATP content was significantly higher in the cold-stress group, but not in the cold-tolerance group. In FW- and SW-acclimated medaka, the expression of genes related to mitochondrial energy metabolism, including pgc-1α, prc, Nrf2, tfam, and nd5, was analyzed to illustrate differential responses of mitochondrial energy metabolism to cold-stress and cold-tolerance environments. When exposed to cold-stress, the relative mRNA expression of pgc-1α, prc, and Nrf2 increased from 2 h, whereas that of tfam and nd5 increased significantly from 168 h. When exposed to a cold-tolerant environment, prc was significantly upregulated at 2 h post-cooling in the FW and SW groups, and pgc-1α was significantly upregulated at 2 and 12 h post-cooling in the FW group, while tfam and nd5 were downregulated in both FW and SW fish. Hierarchical clustering revealed gene interactions in the cold-stress group, which promoted diverse mitochondrial energy adaptations, causing an increase in ATP production. However, the cold-tolerant group demonstrated limitations in enhancing ATP levels through mitochondrial regulation via the PGC-1α energy metabolism pathway. These findings suggest that ectothermic fish may develop varying degrees of thermal tolerance over time in response to climate change. This study provides insights into the complex ways in which fish adjust their metabolism when exposed to cold stress, contributing to our knowledge of how they adapt.

Metabolic consequences of PGC-1α dysregulation in adult zebrafish muscle

The peroxisome proliferator activated receptor gamma co-activator 1 alpha (PGC-1α) is central to the regulation of cellular and mitochondrial energy homeostasis in mammals, but its role in other vertebrates remains unclear. Indeed, previous work suggests extensive structural and functional divergence of PGC-1α in teleosts but this remains to be directly tested. Here, we describe the initial characterization of heterozygous PGC-1α mutant zebrafish lines created by CRISPR-Cas9 disruptions of an evolutionarily conserved regulatory region of the PGC-1α proximal promoter. Using qPCR, we confirmed the disruption of PGC-1α gene expression in striated muscle, leading to a simultaneous 4-fold increase in mixed skeletal muscle PGC-1α mRNA levels and an opposite 4-fold downregulation in cardiac muscle. In mixed skeletal muscle, most downstream effector genes were largely unaffected yet two mitochondrial lipid transporters, carnitine palmitoyltransferase 1 and 2, were strongly induced. Conversely, PGC-1α depression in cardiac muscle reduced the expression of several transcriptional regulators (estrogen related receptor alpha, nuclear respiratory factor 1 and PGC-1β) without altering metabolic gene expression. Using high resolution respirometry, we determined that white muscle exhibited increased lipid oxidative capacity with little difference in markers of mitochondrial abundance. Finally, using whole animal intermittent respirometry, we show that mutant fish exhibit a 2-fold higher basal metabolism than their wildtype counterparts. Altogether, this new model confirms a central but complex role for PGC-1α in mediating energy utilization in zebrafish and we propose its use as a valuable tool to explore the intricate regulatory pathways of energy homeostasis in a popular biomedical model.

Experimental manipulation of microbiota reduces host thermal tolerance and fitness under heat stress in a vertebrate ectotherm

Identifying factors that influence how ectothermic animals respond physiologically to changing temperatures is of high importance given current threats of global climate change. Host-associated microbial communities impact animal physiology and have been shown to influence host thermal tolerance in invertebrate systems. However, the role of commensal microbiota in the thermal tolerance of ectothermic vertebrates is unknown. Here we show that experimentally manipulating the tadpole microbiome through environmental water sterilization reduces the host's acute thermal tolerance to both heat and cold, alters the thermal sensitivity of locomotor performance, and reduces animal survival under prolonged heat stress. We show that these tadpoles have reduced activities of mitochondrial enzymes and altered metabolic rates compared with tadpoles colonized with unmanipulated microbiota, which could underlie differences in thermal phenotypes. These results demonstrate a strong link between the microbiota of an ectothermic vertebrate and the host's thermal tolerance, performance and fitness. It may therefore be important to consider host-associated microbial communities when predicting species' responses to climate change.

Mitochondrial Adaptation to Diet and Swimming Activity in Gilthead Seabream: Improved Nutritional Efficiency

Sustained exercise promotes growth in different fish species, and in gilthead seabream we have demonstrated that it improves nutrient use efficiency. This study assesses for differences in growth rate, tissue composition and energy metabolism in gilthead seabream juveniles fed two diets: high-protein (HP; 54% protein, 15% lipid) or high energy (HE; 50% protein, 20% lipid), under voluntary swimming (VS) or moderate-to-low-intensity sustained swimming (SS) for 6 weeks. HE fed fish under VS conditions showed lower body weight and higher muscle lipid content than HP fed fish, but no differences between the two groups were observed under SS conditions. Irrespective of the swimming regime, the white muscle stable isotopes profile of the HE group revealed increased nitrogen and carbon turnovers. Nitrogen fractionation increased in the HP fed fish under SS, indicating enhanced dietary protein oxidation. Hepatic gene expression markers of energy metabolism and mitochondrial biogenesis showed clear differences between the two diets under VS: a significant shift in the COX/CS ratio, modifications in UCPs, and downregulation of PGC1a in the HE-fed fish. Swimming induced mitochondrial remodeling through upregulation of fusion and fission markers, and removing almost all the differences observed under VS. In the HE-fed fish, white skeletal muscle benefited from the increased energy demand, amending the oxidative uncoupling produced under the VS condition by an excess of lipids and the pro-fission state observed in mitochondria. Contrarily, red muscle revealed more tolerant to the energy content of the HE diet, even under VS conditions, with higher expression of oxidative enzymes (COX and CS) without any sign of mitochondrial stress or mitochondrial biogenesis induction. Furthermore, this tissue had enough plasticity to shift its metabolism under higher energy demand (SS), again equalizing the differences observed between diets under VS condition. Globally, the balance between dietary nutrients affects mitochondrial regulation due to their use as energy fuels, but exercise corrects imbalances allowing practical diets with lower protein and higher lipid content without detrimental effects.

Chronic exposure to anthropogenic and climate related stressors alters transcriptional responses in the liver of zebrafish (Danio rerio) across multiple generations

The antidepressant, venlafaxine (VFX), and climate change stressors, such as increased water temperature and decreased dissolved oxygen, are current threats to aquatic environments. This study aimed to determine how microRNAs (miRNAs) and predicted targeted transcripts were altered in livers of zebrafish exposed to these stressors, and livers of their un-exposed F₁ and F₂ offspring. Following a 21 day exposure to multiple stressors (1 μg/L VFX, +5 °C ambient, 50% O₂), then a subsequent 21 day recovery, relative abundances of cyp3a65, hsp70, hsp90, and ppargc1a and miRNAs predicted to target them (miR-142a, miR-16c, miR-181c, and miR-129, respectively) were measured in the liver via quantitative PCR (RT-qPCR). There were significant decreases in miR-142a in the exposed F₀ generation and the exposed F₁ generation. While there were no changes detected in cyp3a65 relative abundance, there was a significant inverse relationship between cyp3a65 and miR-142a. Hsp70 expression significantly increased in the F₁ generation, which persisted to the F₂ generation and the relative abundance of hsp90 significantly increased in all generations. There was a significant reduction in miR-181c in the F₁ generation, but there was no significant relationship between miR-181c and hsp90. Finally, there was a significant decrease in ppargc1a relative abundance in the F₁ generation which was associated with an increase in miR-129. Combined, these results suggest that parental exposure to multiple, environmentally relevant stressors can confer transcriptional and epigenetic responses in the F₁ and F₂ generations, although identifying which stressor is a driving force becomes unclear.

Climbing Waterfalls: How Metabolism and Behavior Impact Locomotor Performance of Tropical Climbing Gobies on Reunion Island

The life cycle of gobies of the Sicydiinae subfamily depends on climbing waterfalls. Two sympatric sicydiines species from Reunion Island, Sicyopterus lagocephalus (SIL) and Cotylopus acutipinnis (COA), employ different climbing modes. SIL uses a steady "inching" mode interrupted by short rest periods, whereas COA exhibits short "power-burst" undulatory movements punctuated by longer rest periods. Consequently, we explored the relationship between climbing performance and metabolic activity in these two species. We demonstrated that the two climbing modes are supported by different ecophysiological profiles that promote the interspecific variability of locomotor performance. More specifically, SIL performed better than COA during a climbing experiment because of its inching climbing mode, supported by a generally greater metabolic capacity and a higher potential for oxidative metabolism. Interestingly, we did not detect any difference in metabolic fuel storage and lactate production during climbing in either species, suggesting that these species can maintain fuel reserves and limit lactate accumulation through extensive rest times. Overall, this study provides new insights into the ecophysiology of these two emblematic species and suggests that the better climbing capacity of SIL is supported by its muscular metabolic capacity.

Molecular Characterization of PGC-1β (PPAR Gamma Coactivator 1β) and its Roles in Mitochondrial Biogenesis in Blunt Snout Bream (Megalobrama amblycephala)

This study aimed at achieving the molecular characterization of peroxisome proliferator-activated receptor-gamma coactivator 1β (PGC-1β) and exploring its modulatory roles in mitochondria biogenesis in blunt snout bream (Megalobrama amblycephala). A full-length cDNA of PGC-1β was cloned from liver which covered 3110 bp encoding 859 amino acids. The conserved motifs of PGC-1β family proteins were gained by MEME software, and the phylogenetic analyses showed motif loss and rearrangement of PGC-1β in fish. The function of PGC-1β was evaluated through overexpression and knockdown of PGC-1β in primary hepatocytes of blunt snout bream. We observed overexpression of PGC-1β along with enhanced mitochondrial transcription factor A (TFAM) expression and mtDNA copies in hepatocytes, and its knockdown led to slightly reduced NRF1 expression. However, knockdown of PGC-1β did not significantly influence TFAM expression or mtDNA copies. The alterations in mitochondria biogenesis were assessed following high-fat intake, and the results showed that it induces downregulation of PGC-1β. Furthermore, significant decreases in mitochondrial respiratory chain activities and mitochondria biogenesis were observed by high-fat intake. Our findings demonstrated that overexpression of PGC-1β induces the enhancement of TFAM expression and mtDNA amount but not NRF-1. Therefore, it could be concluded that PGC-1β is involved in mitochondrial biogenesis in blunt snout bream but not through PGC-1β/NRF-1 pathway.

Changes in hypothermal stress-induced hepatic mitochondrial metabolic patterns between fresh water- and seawater-acclimated milkfish, Chanos chanos

Milkfish (Chanos chanos) is a tropical euryhaline species. It can acclimate to fresh water (FW) or seawater (SW) and be cultured in both. In winter, cold snaps cause huge losses in milkfish revenue. Compared to FW-acclimated individuals, SW-acclimated milkfish have better low-temperature tolerance. Under hypothermal stress, a stable energy supply is critical to maintain normal liver function. In this study, the levels of key mitochondrial enzymes (citrate synthase (CS) and cytochrome c oxidase (COX)) in milkfish livers were examined. The CS:COX activity ratio in FW milkfish significantly increased under hypothermal stress (18 °C) whereas ATP (the end product of aerobic metabolism) was downregulated. Therefore, the activities of the enzymes involved in mitochondrial amino acid biosynthesis (aspartate aminotransferase (AST) and glutamate dehydrogenase (GDH)) were evaluated to elucidate energy flow in milkfish livers under hypothermal stress. In FW milkfish, GDH activity was upregulated whereas AST activity was downregulated. Nevertheless, the levels of all the aforementioned enzymes did not significantly change in SW milkfish under hypothermal stress. In summary, we clarified the mechanism accounting for the fact that SW milkfish have superior low-temperature tolerance to FW milkfish and demonstrated that SW and FW milkfish have different and unique strategies for regulating energy flow.

Alterations in the Mitochondrial Physiology of Biomphalaria glabrata (Mollusca: Gastropoda) After Experimental Infection by Angiostrongylus cantonensis (Nematoda: Metastrongylidae)

BACKGROUND

Angiostrongylus cantonensis is a metastrongylid nematode that has a heteroxenous cycle, where snails act as intermediate hosts and the rodents Rattus rattus and Rattus novergicus are the definitive hosts. However, humans may act as accidental hosts presenting an atypical form of parasitism. This fact has motivated research to better understand systems of relationships involving A. cantonensis, targeting the control of species of gastropods that act as intermediary hosts.

METHODS

For this, six groups were formed: three control groups (uninfected) and three infected groups, exposed to approximately 1200 L1 larvae of A. cantonensis. At the end of each week (1, 2, and 3 weeks), snails were dissected without anesthesia and the gonad-digestive gland (DGG) complex was separated for determination of oxygen consumption through high-resolution titration-injection respirometer (Oroboros, Oxygraph; Innsbruck, Austria).

RESULTS

The results indicate suppression of mitochondrial oxidative metabolism of the host and compromised in different mitochondrial respiratory states. This effect, mainly observed in the group exposed to 1 week of infection, showed a decrease of approximately 38% (2.78 ± 0.37 pmol O2/mg of tissue; P < 0.05), 41% (2.76 ± 0.34 pmol O2/mg of tissue; P < 0.05) e 46% (2.91 ± 0.36 pmol O2/mg of tissue; P < 0.05) in the basal oxygen consumption after sequential addition (P + M), succinate and (ADP) in the respiratory medium, differing significantly from the control group.

CONCLUSION

The results presented indicate that the prepatent infection by this metastrongylid impairs the aerobic oxidative metabolism of its host, causing a reduction in basal oxygen consumption. This effect, observed at the start of development of the parasites, indicates that this stage is the most critical for the success of the infection, and can be explained by a reduction of the mitochondrial density of the tissue analyzed, or also by suppression of enzyme centers related to the oxidative reactions.

Metabolic regulation by the PGC-1α and PGC-1β coactivators in larval zebrafish (Danio rerio)

The peroxisome proliferator activated receptor γ coactivator-1 (PGC-1) family is composed of three coactivators whose role in regulating mammalian bioenergetics regulation is clear, but is much less certain in other vertebrates. Current evidence suggests that in fish, PGC-1α and PGC-1β may exhibit much less redundancy in the control of fatty acid oxidation and mitochondrial biogenesis compared to mammals. To assess these roles directly, we knocked down PGC-1α and PGC-1β expression with morpholinos in zebrafish embryos, and we investigated the resulting molecular and physiological phenotypes. First, we found no effects of either morpholinos on larval hatching, heart rates and oxygen consumption over the first few days of development. Next, at 3 days post fertilization (dpf), we confirmed by real time PCR a specific knock down of both coactivators, that resulted in a significant reduction in the transcript levels of citrate synthase (CS), 3-hydroxyacyl-CoA dehydrogenase (HOAD), and medium-chain acyl-coenzyme A dehydrogenase (MCAD) in both morphant groups. However, there was no effect on transcription factors' gene expression except for a marked reduction in estrogen related receptor α (ERRα) transcripts in PGC-1α morphants. Finally, we assessed whole embryonic enzyme activity for CS, cytochrome oxidase (COX), HOAD and carnitine palmitoyltransferase I (CPT-1) at 4 dpf. The only significant effect of the knockdown was a reduced CS activity in PGC-1α morphants and a counterintuitive increase of cytochrome oxidase activity in PGC-1β morphants. Overall, our results indicate that in larval zebrafish, PGC-1α and PGC-1β both play a role in regulating expression of important mitochondrial genes potentially through ERRα.

Histone deacetylase activity mediates thermal plasticity in zebrafish (Danio rerio)

Regulatory mechanisms underlying thermal plasticity determine its evolution and potential to confer resilience to climate change. Here we show that class I and II histone deacetylases (HDAC) mediated thermal plasticity globally by shifting metabolomic profiles of cold acclimated zebrafish (Danio rerio) away from warm acclimated animals. HDAC activity promoted swimming performance, but reduced slow and fast myosin heavy chain content in cardiac and skeletal muscle. HDAC increased sarco-endoplasmic reticulum ATPase activity in cold-acclimated fish but not in warm-acclimated animals, and it promoted cardiac function (heart rate and relative stroke volume) in cold but not in warm-acclimated animals. HDAC are an evolutionarily ancient group of proteins, and our data show that they mediate the capacity for thermal plasticity, although the actual manifestation of plasticity is likely to be determined by interactions with other regulators such as AMP-activated protein kinase and thyroid hormone.

Variation in Thermal Tolerance and Its Relationship to Mitochondrial Function Across Populations of Tigriopus californicus

Variation in thermal tolerance plays a key role in determining the biogeographic distribution of organisms. Consequently, identifying the mechanistic basis for thermal tolerance is necessary for understanding not only current species range limits but also the capacity for range limits to shift in response to climate change. Although variation in mitochondrial function likely contributes to variation in thermal tolerance, the extent to which mitochondrial function underlies local thermal adaptation is not fully understood. In the current study, we examine variation in thermal tolerance and mitochondrial function among three populations of the intertidal copepod Tigriopus californicus found across a latitudinal thermal gradient along the coast of California, USA. We tested (1) acute thermal tolerance using survivorship and knockdown assays, (2) chronic thermal tolerance using survivorship of nauplii and developmental rate, and (3) mitochondrial performance at a range of temperatures using ATP synthesis fueled by complexes I, II, and I&II, as well as respiration of permeabilized fibers. We find evidence for latitudinal thermal adaptation: the southernmost San Diego population outperforms the northernmost Santa Cruz in measures of survivorship, knockdown temperature, and ATP synthesis rates during acute thermal exposures. However, under a chronic thermal regime, survivorship and developmental rate are more similar in the southernmost and northernmost population than in the mid-range population (Abalone Cove). Though this pattern is unexpected, it aligns well with population-specific rates of ATP synthesis at these chronic temperatures. Combined with the tight correlation of ATP synthesis decline and knockdown temperature, these data suggest a role for mitochondria in setting thermal range limits and indicate that divergence in mitochondrial function is likely a component of adaptation across latitudinal thermal gradients.

Molecular Characterization of Peroxisome Proliferator-Activated Receptor-Gamma Coactivator-1α (PGC1α) and Its Role in Mitochondrial Biogenesis in Blunt Snout Bream (Megalobrama amblycephala)

PGC1α is a transcriptional coactivator that plays key roles in mitochondrial biogenesis, so exploring its molecular characterization contributes to the understanding of mitochondrial function in cultured fish. In the present study, a full-length cDNA coding PGC1α was cloned from the liver of blunt snout bream (Megalobrama amblycephala) which covered 3741 bp with an open reading frame of 2646 bp encoding 881 amino acids. Sequence alignment and phylogenetic analysis revealed high conservation with other fish species, as well as other higher vertebrates. Comparison of the derived amino acid sequences indicates that, as with other fish, there is a proline at position 176 (RIRP) compared to a Thr in the mammalian sequences (RIRT). To investigate PGC1α function, three in vitro tests were carried out using primary hepatocytes of blunt snout bream. The effect of AMPK activity on the expression of PGC1α was determined by the culture of the hepatocytes with an activator (Metformin) or inhibitor (Compound C) of AMPK. Neither AMPK activation nor inhibition altered PGC1α expression. Knockdown of PGC1α expression in hepatocytes using small interfering RNA (si-RNA) was used to determine the role of PGC1α in mitochondrial biogenesis. No significant differences in the expression of NRF1 and TFAM, and mtDNA copy number were found between control and si-RNA groups. Also, hepatocytes were cultured with oleic acid, and the findings showed the significant reduction of mtDNA copy number in oleic acid group compared to control. Moreover, oleic acid down-regulated the expression of NRF1 and TFAM genes, while PGC1α expression remained unchanged. Our findings support the proposal that PGC1α may not play a role in mitochondrial biogenesis in blunt snout bream hepatocytes.

Benfotiamine, a Lipid-Soluble Analog of Vitamin B1, Improves the Mitochondrial Biogenesis and Function in Blunt Snout Bream (Megalobrama amblycephala) Fed High-Carbohydrate Diets by Promoting the AMPK/PGC-1β/NRF-1 Axis

This study evaluated the effects of benfotiamine on the growth performance and mitochondrial biogenesis and function in Megalobrama amblycephala fed high-carbohydrate (HC) diets. The fish (45.25 ± 0.34 g) were randomly fed six diets: the control diet (30% carbohydrate, C), the HC diet (43% carbohydrate), and the HC diet supplemented with different benfotiamine levels (0.7125 (HCB1), 1.425 (HCB2), 2.85 (HCB3), and 5.7 (HCB4) mg/kg) for 12 weeks. High-carbohydrate levels remarkably decreased the weight gain rate (WGR), specific growth rate (SGR), relative feed intake (RFI), feed conversion ratio (FCR), p-adenosine monophosphate (AMP)-activated protein kinase (AMPK)α/t-AMPKα ratio, peroxisome proliferator-activated receptor-γ coactivator-1β (PGC-1β) and nuclear respiratory factor-1 (NRF-1) protein expression, complexes I, III, and IV activities, and hepatic transcriptions of cytochrome b (CYT-b) and cytochrome c oxidase-2 (COX-2), whereas the opposite was true for plasma glucose, glycated serum protein, advanced glycation end product and insulin levels, tissue glycogen and lipid contents, hepatic adenosine triphosphate (ATP) and AMP contents and ATP/AMP ratio, complexes V activities, and the expressions of AMPKα-2, PGC-1β, NRF-1, mitochondrial transcription factor A (TFAM), mitofusin-1 (Mfn-1), optic atrophy-1 (Opa-1), dynamin-related protein-1 (Drp-1), fission-1 (Fis-1), mitochondrial fission factor (Mff), and ATP synthase-6 (ATP-6). As with benfotiamine supplementation, the HCB2 diet remarkably increased WGR, SGR, tissue glycogen and lipid contents, AMP content, p-AMPKα/t-AMPKα ratio, PGC-1β and NRF-1 levels, complexes I, III, IV, and V activities, and hepatic transcriptions of AMPKα-2, PGC-1β, NRF-1, TFAM, Mfn-1, Opa-1, CYT-b, COX-2, and ATP-6, while the opposite was true for the remaining indicators. Overall, 1.425 mg/kg benfotiamine improved the growth performance and mitochondrial biogenesis and function in fish fed HC diets by the activation of the AMPK/PGC-1β/NRF-1 axis and the upregulation of the activities and transcriptions of mitochondrial complexes as well as the enhancement of mitochondrial fusion coupled with the depression of mitochondrial fission.

Exercise-Induced Hypertrophic and Oxidative Signaling Pathways and Myokine Expression in Fast Muscle of Adult Zebrafish

Skeletal muscle is a plastic tissue that undergoes cellular and metabolic adaptations under conditions of increased contractile activity such as exercise. Using adult zebrafish as an exercise model, we previously demonstrated that swimming training stimulates hypertrophy and vascularization of fast muscle fibers, consistent with the known muscle growth-promoting effects of exercise and with the resulting increased aerobic capacity of this tissue. Here we investigated the potential involvement of factors and signaling mechanisms that could be responsible for exercise-induced fast muscle remodeling in adult zebrafish. By subjecting zebrafish to swimming-induced exercise, we observed an increase in the activity of mammalian target of rapamycin (mTOR) and Mef2 protein levels in fast muscle. We also observed an increase in the protein levels of the mitotic marker phosphorylated histone H3 that correlated with an increase in the protein expression levels of Pax7, a satellite-like cell marker. Furthermore, the activity of AMP-activated protein kinase (AMPK) was also increased by exercise, in parallel with an increase in the mRNA expression levels of pgc1α and also of pparda, a β-oxidation marker. Changes in the mRNA expression levels of slow and fast myosin markers further supported the notion of an exercise-induced aerobic phenotype in zebrafish fast muscle. The mRNA expression levels of il6, il6r, apln, aplnra and aplnrb, sparc, decorin and igf1, myokines known in mammals to be produced in response to exercise and to signal through mTOR/AMPK pathways, among others, were increased in fast muscle of exercised zebrafish. These results support the notion that exercise increases skeletal muscle growth and myogenesis in adult zebrafish through the coordinated activation of the mTOR-MEF2 and AMPK-PGC1α signaling pathways. These results, coupled with altered expression of markers for oxidative metabolism and fast-to-slow fiber-type switch, also suggest improved aerobic capacity as a result of swimming-induced exercise. Finally, the induction of myokine expression by swimming-induced exercise support the hypothesis that these myokines may have been produced and secreted by the exercised zebrafish muscle and acted on fast muscle cells to promote metabolic remodeling. These results support the use of zebrafish as a suitable model for studies on muscle remodeling in vertebrates, including humans.

Comparative biochemistry of cytochrome c oxidase in animals

Cytochrome c oxidase (COX), the terminal enzyme of the electron transport system, is central to aerobic metabolism of animals. Many aspects of its structure and function are highly conserved, yet, paradoxically, it is also an important model for studying the evolution of the metabolic phenotype. In this review, part of a special issue honouring Peter Hochachka, we consider the biology of COX from the perspective of comparative and evolutionary biochemistry. The approach is to consider what is known about the enzyme in the context of conventional biochemistry, but focus on how evolutionary researchers have used this background to explore the role of the enzyme in biochemical adaptation of animals. In synthesizing the conventional and evolutionary biochemistry, we hope to identify synergies and future research opportunities. COX represents a rare opportunity for researchers to design studies that span the breadth of biology: molecular genetics, protein biochemistry, enzymology, metabolic physiology, organismal performance, evolutionary biology, and phylogeography.

Exogenous thyroid hormones regulate the activity of citrate synthase and cytochrome c oxidase in warm- but not cold-acclimated lake whitefish (Coregonus clupeaformis)

Thermal acclimation is known to elicit metabolic adjustments in ectotherms, but the cellular mechanisms and endocrine control of these shifts have not been fully elucidated. Here we examined the relationship between thermal acclimation, thyroid hormones and oxidative metabolism in juvenile lake whitefish. Impacts of thermal acclimation above (19°C) or below (8°C) the thermal optimum (13°C) and exposure to exogenous thyroid hormone (60µg T₄/g body weight) were assessed by quantifying citrate synthase and cytochrome c oxidase activities in liver, red muscle, white muscle and heart. Warm acclimation decreased citrate synthase activity in liver and elevated both citrate synthase and cytochrome c oxidase activities in red muscle. In contrast, induction of hyperthyroidism in warm-acclimated fish stimulated a significant increase in liver citrate synthase and heart cytochrome c oxidase activities, and a decrease in the activity of both enzymes in red muscle. No change in citrate synthase or cytochrome c oxidase activities was observed following cold acclimation in either the presence or absence of exogenous thyroid hormones. Collectively, our results indicate that thyroid hormones influence the activity of oxidative enzymes more strongly in warm-acclimated than in cold-acclimated lake whitefish, and they may play a role in mediating metabolic adjustments observed during thermal acclimation.

Metabolic and regulatory responses involved in cold acclimation in Atlantic killifish, Fundulus heteroclitus

Ectotherms often respond to prolonged cold exposure by increasing mitochondrial capacity via elevated mitochondrial volume density [V _V(mit,f)]. In fish, higher V _V(mit,f) is typically associated with increased expression of nuclear respiratory factor 1 (Nrf1), a transcription factor that induces expression of nuclear-encoded respiratory genes. To examine if nrf1 expression or the expression of other genes that regulate mitochondrial biogenesis contribute to changes in whole-organism metabolic rate during cold acclimation, we examined the time course of changes in the expression of these genes and in metabolic rate in Atlantic killifish, Fundulus heteroclitus. Cold acclimation rapidly decreased metabolic rate, but increased the expression of nrf1 more gradually, with a time course that depended on how rapidly the fish were transitioned to low temperature. Cold-induced nrf1 expression was not associated with increases in biochemical indicators of mitochondrial respiratory capacity, suggesting that cold-induced mitochondrial biogenesis may occur without increases in oxidative capacity in this species. These observations imply that changes in nrf1 expression and metabolic rate due to cold acclimation occur through different physiological mechanisms, and that increases in V _V(mit,f) are likely not directly related to changes in metabolic rate with cold acclimation in this species. However, nrf1 expression differed between northern and southern killifish subspecies regardless of acclimation temperature, consistent with observed differences in metabolic rate and V _V(mit,f) at 5 °C between these subspecies. Taken together, these results reveal substantial complexity in the regulation of V _V(mit,f) and mitochondrial capacity with temperature in fish and the relationship of these parameters to metabolic rate.

Molecular drivers of mitochondrial membrane proliferation in response to cold acclimation in threespine stickleback

Little is known about how the synthesis of mitochondrial phospholipids is integrated into mitochondrial biogenesis in fish or mammals. Glycerol-3-phosphate acyltransferase (GPAT; EC 2.3.1.15) catalyzes the addition of fatty acyl CoA to the sn-1 position of glycerol-3-phosphate, in what is considered the rate-limiting step in phospholipid biosynthesis. Previous studies have shown that mitochondrial volume density increases in oxidative skeletal muscle but not liver of Gasterosteus aculeatus (threespine stickleback) in response to cold acclimation. We hypothesized that maximal activity of GPAT would increase in oxidative skeletal muscle but not liver during cold acclimation, coinciding with mitochondrial biogenesis. GPAT activity was measured in liver and oxidative skeletal (pectoral adductor) muscle of threespine stickleback acclimated to 8°C or 20°C. In addition, mRNA levels of enzymes involved in phospholipid synthesis, including cytidine diphosphodiacylglycerol synthase-1 (CDS1), CDS2, GPAT1, GPAT2 and 1-acylglycerol 3-phosphate acyltransferase-2 (AGPAT2), were quantified in liver and pectoral muscle of stickleback harvested during cold acclimation. GPAT activity and transcript levels of AGPAT2 increased in response to cold acclimation in pectoral muscle but not liver. Transcript levels of GPAT1 increased in liver but not pectoral muscle. Overall our results suggest that the activity of GPAT, and possibly AGPAT as well, increase during cold acclimation and may contribute to mitochondrial phospholipid biosynthesis required for mitochondrial biogenesis.

Mitochondrial biogenesis and clearance: a balancing act

Mitochondria are semi-autonomous organelles of prokaryotic origin that are postulated to have been acquired by eukaryotic cells through an early endosymbiotic event. Except for their main role in energy production, they are also implicated in fundamental cellular processes, including ion homeostasis, lipid metabolism, and initiation of apoptotic cell death. Perturbed mitochondrial function has been correlated with severe human pathologies such as type-2 diabetes, cardiovascular, and neurodegenerative diseases. Thus, proper mitochondrial physiology is a prerequisite for health and survival. Cells have developed sophisticated and elaborate mechanisms to adapt to stress conditions and alterations in metabolic demands, by regulating mitochondrial number and function. Hence, the generation of new and the removal of damaged or unwanted mitochondria are highly regulated processes that need to be accurately coordinated for the maintenance of mitochondrial and cellular homeostasis. Here, we survey recent research findings that advance our understanding and highlight the importance of the underlying molecular mechanisms.

Evaluating the role of NRF-1 in the regulation of the goldfish COX4-1 gene in response to temperature

Cold acclimation in fish typically increases muscle mitochondrial enzymes. In mammals, stressors that increase mitochondrial content are mediated though transcriptional regulators, including nuclear respiratory factor-1 (NRF-1). Focusing on the goldfish gene for cytochrome c oxidase (COX) subunit 4-1, we analysed the regulatory regions in various contexts to identify a mechanistic link between NRF-1 and cold-induced mitochondrial proliferation. Promoter analysis implicated two putative NRF-1 sites: one in the proximal promoter and a second in exon 1, which encodes the 5' untranslated region (5'-UTR). Transfection into mouse myoblasts showed that deletion of a region that included the proximal NRF-1 site reduced promoter activity by 30%; however, mutagenesis of the specific sequence had no effect. Thermal sensitivity analyses performed in rainbow trout gonadal fibroblasts (RTG-2) showed no effect of temperature (4 vs 19°C) on reporter gene expression. Likewise, reporters injected into muscle of thermally acclimated goldfish (4 vs 26°C) showed no elevation in expression. There was no difference in thermal responses of COX4-1 promoter reporters constructed from homologous regions of eurythermal goldfish and stenothermal zebrafish genes. NRF-1 chromatin immunoprecipitation of thermally acclimated goldfish muscle showed no temperature effect on NRF-1 binding to either the proximal promoter or 5'-UTR. It remains possible that the cold-induced upregulation of COX4-1 expression is a result of NRF-1 binding to distal regulatory regions or through indirect effects on other transcription factors. However, the proximal promoter does not appear to play a role in mediating the thermal response of the COX4-1 gene in fish.

WITHDRAWN: Alterations in the mitochondrial physiology of Biomphalaria glabrata (Mollusca: Gastropoda) after experimental infection by Angiostrongylus cantonensis (Nematoda: Metastongylidae)

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Evolution of Plasticity: Mechanistic Link between Development and Reversible Acclimation

Phenotypic characteristics of animals can change independently from changes in the genetic code. These plastic phenotypic responses are important for population persistence in changing environments. Plasticity can be induced during early development, with persistent effects on adult phenotypes, and it can occur reversibly throughout life (acclimation). These manifestations of plasticity have been viewed as separate processes. Here we argue that developmental conditions not only change mean trait values but also modify the capacity for acclimation. Acclimation counteracts the potentially negative effects of phenotype-environment mismatches resulting from epigenetic modifications during early development. Developmental plasticity is therefore also beneficial when environmental conditions change within generations. Hence, the evolution of reversible acclimation can no longer be viewed as independent from developmental processes.

Dietary lipid concentration affects liver mitochondrial DNA copy number, gene expression and DNA methylation in large yellow croaker (Larimichthys crocea)

In response to changes in energy demand and nutrient supply, the organism regulates mitochondrial metabolic status to coordinate ATP production. To survey mitochondrial metabolic adaptation in response to dietary lipid concentration, citrate synthase (EC 2.3.3.1, CS) activity, the expression of several mitochondrial transcription factors, mitochondrial DNA (mtDNA) copy number, mitochondrial gene expression, mtDNA methylation, and oxidative stress parameters were analyzed in the liver of large yellow croaker fed one of three diets with a low (6%), moderate (12%, the control diet) or high (18%) crude lipid content for 70 d. MtDNA copy number was significantly increased in the low- and high-lipid groups compared to the control. The transcription of cytochrome c oxidase 1 (COX1), COX2, COX3, ATP synthase 6 (ATPase 6), 12S rRNA and 16S rRNA was also significantly increased in the low-lipid group compared with the control, while the transcription of these genes in the high-lipid group was unchanged. Moreover, D-loop (displacement loop) methylation in the high-lipid group was significantly higher than the control. The increase in mtDNA copy number and mitochondrial transcription might be a compensatory mechanism that matches ATP supply to demand under a low-lipid diet, while the increase of mtDNA copy number with unchanged mitochondrial transcription in the high-lipid group probably came from the increase of D-loop methylation.

Evolution of urea transporters in vertebrates: adaptation to urea's multiple roles and metabolic sources

In the two decades since the first cloning of the mammalian kidney urea transporter (UT-A), UT genes have been identified in a plethora of organisms, ranging from single-celled bacteria to metazoans. In this review, focusing mainly on vertebrates, we first reiterate the multiple catabolic and anabolic pathways that produce urea, then we reconstruct the phylogenetic history of UTs, and finally we examine the tissue distribution of UTs in selected vertebrate species. Our analysis reveals that from an ancestral UT, three homologues evolved in piscine lineages (UT-A, UT-C and UT-D), followed by a subsequent reduction to a single UT-A in lobe-finned fish and amphibians. A later internal tandem duplication of UT-A occurred in the amniote lineage (UT-A1), followed by a second tandem duplication in mammals to give rise to UT-B. While the expected UT expression is evident in excretory and osmoregulatory tissues in ureotelic taxa, UTs are also expressed ubiquitously in non-ureotelic taxa, and in tissues without a complete ornithine-urea cycle (OUC). We posit that non-OUC production of urea from arginine by arginase, an important pathway to generate ornithine for synthesis of molecules such as polyamines for highly proliferative tissues (e.g. testis, embryos), and neurotransmitters such as glutamate for neural tissues, is an important evolutionary driving force for the expression of UTs in these taxa and tissues.

PGC-1/Spargel Counteracts High-Fat-Diet-Induced Obesity and Cardiac Lipotoxicity Downstream of TOR and Brummer ATGL Lipase

Obesity and metabolic syndrome are associated with an increased risk for lipotoxic cardiomyopathy, which is strongly correlated with excessive accumulation of lipids in the heart. Obesity- and type-2-diabetes-related disorders have been linked to altered expression of the transcriptional cofactor PGC-1α, which regulates the expression of genes involved in energy metabolism. Using Drosophila, we identify PGC-1/spargel (PGC-1/srl) as a key antagonist of high-fat diet (HFD)-induced lipotoxic cardiomyopathy. We find that HFD-induced lipid accumulation and cardiac dysfunction are mimicked by reduced PGC-1/srl function and reversed by PGC-1/srl overexpression. Moreover, HFD feeding lowers PGC-1/srl expression by elevating TOR signaling and inhibiting expression of the Drosophila adipocyte triglyceride lipase (ATGL) (Brummer), both of which function as upstream modulators of PGC-1/srl. The lipogenic transcription factor SREBP also contributes to HFD-induced cardiac lipotoxicity, likely in parallel with PGC-1/srl. These results suggest a regulatory network of key metabolic genes that modulates lipotoxic heart dysfunction.

Effects of salinity on metabolic rate and branchial expression of genes involved in ion transport and metabolism in Mozambique tilapia (Oreochromis mossambicus)

This study investigated the effects of two rearing salinities, and acute salinity transfer, on the energetic costs of osmoregulation and the expression of metabolic and osmoregulatory genes in the gill of Mozambique tilapia. Using automated, intermittent-flow respirometry, measured standard metabolic rates (SMRs) of tilapia reared in seawater (SW, 130 mg O₂ kg⁻¹ h⁻¹) were greater than those reared in fresh water (FW, 103 mg O₂ kg⁻¹ h⁻¹), when normalized to a common mass of 0.05 kg and at 25±1°C. Transfer from FW to 75% SW increased SMR within 18h, to levels similar to SW-reared fish, while transfer from SW to FW decreased SMR to levels similar to FW-reared fish. Branchial gene expression of Na⁺-K⁺-2Cl⁻ cotransporter (NKCC), an indicator of SW-type mitochondria-rich (MR) cells, was positively correlated with SMR, while Na⁺-Cl⁻ cotransporter (NCC), an indicator of FW-type MR cells, was negatively correlated. Principal Components Analysis also revealed that branchial expression of cytochrome c oxidase subunit IV (COX-IV), glycogen phosphorylase (GP), and a putative mitochondrial biogenesis regulator in fish, peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α), were correlated with a higher SMR, plasma osmolality, and environmental salinity, while expression of glycogen synthase (GS), PGC-1β, and nuclear respiratory factor 1 (NRF-1) had negative correlations. These results suggest that the energetic costs of osmoregulation are higher in SW than in FW, which may be related to the salinity-dependent differences in osmoregulatory mechanisms found in the gills of Mozambique tilapia.

Energy metabolism and cytochrome oxidase activity: linking metabolism to gene expression

Modification of mitochondrial content demands the synthesis of hundreds of proteins encoded by nuclear and mitochondrial genomes. The responsibility for coordination of this process falls to nuclear-encoded master regulators of transcription. DNA-binding proteins and coactivators integrate information from energy-sensing pathways and hormones to alter mitochondrial gene expression. In mammals, the signaling cascade for mitochondrial biogenesis can be described as follows: hormonal signals and energetic information are sensed by protein-modifying enzymes that in turn regulate the post-translational modification of transcription factors. Once activated, transcription-factor complexes form on promoter elements of many of the nuclear-encoded mitochondrial genes, recruiting proteins that remodel chromatin and initiate transcription. One master regulator in mammals, PGC-1α, is well studied because of its role in determining the metabolic phenotype of muscles, but also due to its importance in mitochondria-related metabolic diseases. However, relatively little is known about the role of this pathway in other vertebrates. These uncertainties raise broader questions about the evolutionary origins of the pathway and its role in generating the diversity in muscle metabolic phenotypes seen in nature.

mRNA degradation: an underestimated factor in steady-state transcript levels of cytochrome c oxidase subunits?

Steady-state mRNA levels are determined by synthesis and degradation; however, changes in mRNA levels are usually attributed to transcription. For cytochrome c oxidase (COX), cold acclimation typically leads to an increase in COX activity while transcript levels for the nuclear-encoded subunits change non-stoichiometrically. Whether those patterns are caused by differences in subunit transcription rates, decay rates or both was not known. We assessed decay rates of transcripts for COX subunits, including representatives that decreased, increased in parallel with COX or increased in excess of COX. Low temperature reduced the decay rate of all transcripts; however, COX subunits displayed higher thermal sensitivity than housekeeping genes. The lower decay rates for COX transcripts might explain some of their increase in response to cold acclimation. The reason for the exaggerated transcript response of two subunits (COX6B-1 and COX7A-2) may be due to decreased decay. However, decay rate differences could not explain the patterns seen with another subunit that did not change in mRNA level with thermal acclimation (COX6A-2). Further, the decay patterns differed between two thermal acclimation experiments, which may explain some of the heterogeneity seen in fish studies. The differences in decay rates suggest that the lack of stoichiometry in mRNA levels is exacerbated by post-transcriptional mechanisms. Collectively, these results suggest that temperature-induced differences in COX subunit mRNA levels and deviations from stoichiometry between them may partially arise from subunit-specific sensitivities to degradation. We suggest that all subunits are controlled by transcription, and that exaggerated responses of some subunits are due to reduced decay rates.

Cold acclimation increases mitochondrial oxidative capacity without inducing mitochondrial uncoupling in goldfish white skeletal muscle

Goldfish have been used for cold acclimation studies, which have focused on changes in glycolytic and oxidative enzymes or alterations in lipid composition in skeletal muscle. Here we examine the effects of cold acclimation on the functional properties of isolated mitochondria and permeabilized fibers from goldfish white skeletal muscle, focusing on understanding the types of changes that occur in the mitochondrial respiratory states. We observed that cold acclimation promoted a significant increase in the mitochondrial oxygen consumption rates. Western blot analysis showed that UCP3 was raised by ∼1.5-fold in cold-acclimated muscle mitochondria. Similarly, we also evidenced a rise in the adenine nucleotide translocase content in cold-acclimated muscle mitochondria compared to warm-acclimated mitochondria (0.96±0.05 vs 0.68±0.02 nmol carboxyatractyloside mg(-1) protein). This was followed by a 2-fold increment in the citrate synthase activity, which suggests a higher mitochondrial content in cold-acclimated goldfish. Even with higher levels of UCP3 and ANT, the effects of activator (palmitate) and inhibitors (carboxyatractyloside and GDP) on mitochondrial parameters were similar in both warm- and cold-acclimated goldfish. Thus, we propose that cold acclimation in goldfish promotes an increase in functional oxidative capacity, with higher mitochondrial content without changes in the mitochondrial uncoupling pathways.

Muscle remodeling and the exercise physiology of fish

Fish muscle responds to aerobic exercise training and cold acclimation with a more aerobic muscle phenotype than mammalian muscle but through both conserved and distinct molecular events. Differences from mammals in exercise metabolism and diversity in protein isoforms suggest that the regulation of muscle fuel use is more complex in fish. This review considers fish as powerful models for exercise and muscle physiology.

Temperature during embryonic development has persistent effects on thermal acclimation capacity in zebrafish

Global warming is intensifying interest in the mechanisms enabling ectothermic animals to adjust physiological performance and cope with temperature change. Here we show that embryonic temperature can have dramatic and persistent effects on thermal acclimation capacity at multiple levels of biological organization. Zebrafish embryos were incubated until hatching at control temperature (T(E) = 27 °C) or near the extremes for normal development (T(E) = 22 °C or 32 °C) and were then raised to adulthood under common conditions at 27 °C. Short-term temperature challenge affected aerobic exercise performance (U(crit)), but each T(E) group had reduced thermal sensitivity at its respective T(E). In contrast, unexpected differences arose after long-term acclimation to 16 °C, when performance in the cold was ∼20% higher in both 32 °C and 22 °C T(E) groups compared with 27 °C T(E) controls. Differences in performance after acclimation to cold or warm (34 °C) temperatures were partially explained by variation in fiber type composition in the swimming muscle. Cold acclimation changed the abundance of 3,452 of 19,712 unique and unambiguously identified transcripts detected in the fast muscle using RNA-Seq. Principal components analysis differentiated the general transcriptional responses to cold of the 27 °C and 32 °C T(E) groups. Differences in expression were observed for individual genes involved in energy metabolism, angiogenesis, cell stress, muscle contraction and remodeling, and apoptosis. Therefore, thermal acclimation capacity is not fixed and can be modified by temperature during early development. Developmental plasticity may thus help some ectothermic organisms cope with the more variable temperatures that are expected under future climate-change scenarios.

Sesamin modulates gene expression without corresponding effects on fatty acids in Atlantic salmon (Salmo salar L.)

This study examined the effects of sesamin inclusion in vegetable oil-based diets fed to Atlantic salmon (Salmo salar L.). The diets used differed in n-6/n-3 fatty acid (FA) ratio (0.5 and 1) and sesamin content (high 5.8 g/kg, low 1.16 g/kg and no sesamin). The oils used in the feeds were a mixture of rapeseed, linseed and palm oil. Fish were fed for 4 months. Fatty acids and expression of hepatic genes involved in transcription, lipid uptake, desaturation, elongation and β-oxidation were measured. No major effects on the percentage of DHA in white muscle, liver triacylglycerol and phospholipid fraction were detected. Genes involved in β-oxidation, elongation and desaturation were affected by sesamin addition. Limited effects were seen on any of the transcription factors tested and no effect was seen on the expression of peroxisome proliferator-activated receptors (PPAR). Expression of both SREBP-1 and SREBP-2 increased with sesamin addition. It was concluded that supplementation of fish feed with a high level of sesamin had a negative effect on the growth rate and live weight and did not alter the proportions of DHA in tissues even though gene expression was affected. Thus, more studies are needed to formulate a diet that would increase the percentage of DHA in fish without negative effects on fish growth.