Untargeted metabolic profiling reveals distinct patterns of thermal sensitivity in two related notothenioids

Circadian rhythm in turbot (Scophthalmus maximus): daily variation of blood metabolites in recirculating aquaculture systems

INTRODUCTION

Animal welfare in aquaculture is becoming increasingly important, and detailed knowledge of the species concerned is essential for further optimization on farms. Every organism is controlled by an internal clock, the circadian rhythm, which is crucial for metabolic processes and is partially influenced by abiotic factors, making it important for aquaculture practices.

OBJECTIVE

In order to determine the circadian rhythm of adult turbot (Scophthalmus maximus), blood samples were collected over a 24-h period and plasma metabolite profiles were analyzed by 1H-NMR spectroscopy.

METHODS

The fish were habituated to feeding times at 9 am and 3 pm and with the NMR spectroscopy 46 metabolites could be identified, eight of which appeared to shift throughout the day.

RESULTS

We noted exceptionally high values around 3 pm for the amino acids isoleucine, leucine, valine, phenylalanine, lysine, and the stress indicator lactate. These metabolic peaks were interpreted as either habituation to the usual feeding time or as natural peak levels in turbot in a 24-h circle because other indicators for stress (glucose, cortisol and lysozymes) showed a stable baseline, indicating that the animals had no or very little stress during the experimental period.

CONCLUSION

This study provides initial insights into the diurnal variation of metabolites in adult turbot; however, further studies are needed to confirm present findings of possible fluctuations in amino acids and sugars. Implementing optimized feeding times (with high levels of sugars and low levels of stress metabolites) could lead to less stress, fewer disease outbreaks and overall improved fish welfare in aquaculture facilities.

Evolutionary Adaptation of Protein Turnover in White Muscle of Stenothermal Antarctic Fish: Elevated Cold Compensation at Reduced Thermal Responsiveness

Protein turnover is highly energy consuming and overall relates to an organism's growth performance varying largely between species, e.g., due to pre-adaptation to environmental characteristics such as temperature. Here, we determined protein synthesis rates and capacity of protein degradation in white muscle of the cold stenothermal Antarctic eelpout (Pachycara brachycephalum) and its closely related temperate counterpart, the eurythermal common eelpout (Zoarces viviparus). Both species were exposed to acute warming (P. brachycephalum, 0 °C + 2 °C day-1; Z. viviparus, 4 °C + 3 °C day-1). The in vivo protein synthesis rate (Ks) was monitored after injection of 13C-phenylalanine, and protein degradation capacity was quantified by measuring the activity of cathepsin D in vitro. Untargeted metabolic profiling by nuclear magnetic resonance (NMR) spectroscopy was used to identify the metabolic processes involved. Independent of temperature, the protein synthesis rate was higher in P. brachycephalum (Ks = 0.38-0.614 % day-1) than in Z. viviparus (Ks= 0.148-0.379% day-1). Whereas protein synthesis remained unaffected by temperature in the Antarctic species, protein synthesis in Z. viviparus increased to near the thermal optimum (16 °C) and tended to fall at higher temperatures. Most strikingly, capacities for protein degradation were about ten times higher in the Antarctic compared to the temperate species. These differences are mirrored in the metabolic profiles, with significantly higher levels of complex and essential amino acids in the free cytosolic pool of the Antarctic congener. Together, the results clearly indicate a highly cold-compensated protein turnover in the Antarctic eelpout compared to its temperate confamilial. Constant versus variable environments are mirrored in rigid versus plastic functional responses of the protein synthesis machinery.

Heat hardening enhances metabolite-driven thermoprotection in the Mediterranean mussel Mytilus galloprovincialis

Introduction: Temperature affects organisms' metabolism and ecological performance. Owing to climate change, sea warming constituting a severe source of environmental stress for marine organisms, since it increases at alarming rates. Rapid warming can exceed resilience of marine organisms leading to fitness loss and mortality. However, organisms can improve their thermal tolerance when briefly exposed to sublethal thermal stress (heat hardening), thus generating heat tolerant phenotypes. Methods: We investigated the "stress memory" effect caused by heat hardening on M. galloprovincialis metabolite profile of in order to identify the underlying biochemical mechanisms, which enhance mussels' thermal tolerance. Results: The heat hardening led to accumulation of amino acids (e.g., leucine, isoleucine and valine), including osmolytes and cytoprotective agents with antioxidant and anti-inflammatory properties that can contribute to thermal protection of the mussels. Moreover, proteolysis was inhibited and protein turnover regulated by the heat hardening. Heat stress alters the metabolic profile of heat stressed mussels, benefiting the heat-hardened individuals in increasing their heat tolerance compared to the non-heat-hardened ones. Discussion: These findings provide new insights in the metabolic mechanisms that may reinforce mussels' tolerance against thermal stress providing both natural protection and potential manipulative tools (e.g., in aquaculture) against the devastating climate change effects on marine organisms.

1H-NMR-Based Metabolic Profiling in Muscle and Liver Tissue of Juvenile Turbot (Scophthalmus maximus) Fed with Plant and Animal Protein Sources

Circular economy driven feed ingredients and emerging protein sources, such as insects and microbial meals, has the potential to partially replace fishmeal in diets of high-trophic fish. Even though growth and feed performance are often unaffected at low inclusion levels, the metabolic effects are unknown. This study examined the metabolic response of juvenile turbot (Scophthalmus maximus) to diets with graded fishmeal replacement with plant, animal, and emerging protein sources (PLANT, PAP, and MIX) in comparison to a commercial-like diet (CTRL). A ¹H-nuclear magnetic resonance (NMR) spectroscopy was used to assess the metabolic profiles of muscle and liver tissue after feeding the fish the experimental diets for 16 weeks. The comparative approach revealed a decrease in metabolites that are associated with energy deficiency in both tissues of fish fed with fishmeal-reduced diets compared to the commercial-like diet (CTRL). Since growth and feeding performance were unaffected, the observed metabolic response suggests that the balanced feed formulations, especially at lower fishmeal replacement levels, have the potential for industry application.

Metabolic remodeling caused by heat hardening in the Mediterranean mussel Mytilus galloprovincialis

Organisms can modify and increase their thermal tolerance faster and more efficiently after a brief exposure to sublethal thermal stress. This response is called 'heat hardening' as it leads to the generation of phenotypes with increased heat tolerance. The aim of this study was to investigate the impact of heat hardening on the metabolomic profile of Mytilus galloprovincialis in order to identify the associated adjustments of biochemical pathways that might benefit the mussels' thermal tolerance. Thus, mussels were exposed sequentially to two different phases (heat hardening and acclimation phases). To gain further insight into the possible mechanisms underlying the metabolic response of the heat-hardened M. galloprovincialis, metabolomics analysis was complemented by the estimation of mRNA expression of phosphoenolpyruvate carboxykinase (PEPCK), pyruvate kinase (PK) and alternative oxidase (AOX) implicated in the metabolic pathways of gluconeogenesis, glycolysis and redox homeostasis, respectively. Heat-hardened mussels showed evidence of higher activity of the tricarboxylic acid (TCA) cycle and diversification of upregulated metabolic pathways, possibly as a mechanism to increase ATP production and extend survival under heat stress. Moreover, formate and taurine accumulation provide an antioxidant and cytoprotective role in mussels during hypoxia and thermal stress. Overall, the metabolic responses in non-heat-hardened and heat-hardened mussels underline the upper thermal limits of M. galloprovincialis, set at 26°C, and are in accordance with the OCLTT concept. The ability of heat-hardened mussels to undergo a rapid gain and slow loss of heat tolerance may be an advantageous strategy for coping with intermittent and often extreme temperatures.

Temperature but not ocean acidification affects energy metabolism and enzyme activities in the blue mussel, Mytilus edulis

In mosaic marine habitats, such as intertidal zones, ocean acidification (OA) is exacerbated by high variability of pH, temperature, and biological CO2 production. The nonlinear interactions among these drivers can be context-specific and their effect on organisms in these habitats remains largely unknown, warranting further investigation.We were particularly interested in Mytilus edulis (the blue mussel) from intertidal zones of the Gulf of Maine (GOM), USA, for this study. GOM is a hot spot of global climate change (average sea surface temperature (SST) increasing by >0.2°C/year) with >60% decline in mussel population over the past 40 years.Here, we utilize bioenergetic underpinnings to identify limits of stress tolerance in M. edulis from GOM exposed to warming and OA. We have measured whole-organism oxygen consumption rates and metabolic biomarkers in mussels exposed to control and elevated temperatures (10 vs. 15°C, respectively) and current and moderately elevated P CO2 levels (~400 vs. 800 µatm, respectively).Our study demonstrates that adult M. edulis from GOM are metabolically resilient to the moderate OA scenario but responsive to warming as seen in changes in metabolic rate, energy reserves (total lipids), metabolite profiles (glucose and osmolyte dimethyl amine), and enzyme activities (carbonic anhydrase and calcium ATPase).Our results are in agreement with recent literature that OA scenarios for the next 100-300 years do not affect this species, possibly as a consequence of maintaining its in vivo acid-base balance.

Characterization of the hypoxia-inducible factor-1 pathway in hearts of Antarctic notothenioid fishes

The ability of Antarctic notothenioid fishes to mount a robust molecular response to hypoxia is largely unknown. The transcription factor, hypoxia-inducible factor-1 (HIF-1), a heterodimer of HIF-1α and HIF-1β subunits, is the master regulator of oxygen homeostasis in most metazoans. We sought to determine if, in the hearts of Antarctic notothenioids, HIF-1 is activated and functional in response to either an acute heat stress or hypoxia. The red-blooded Notothenia coriiceps and the hemoglobinless icefish, Chaenocephalus aceratus, were exposed to their critical thermal maximum (CT_MAX) or hypoxia (5.0 ± 0.3 mg of O₂ L^-1) for 2 h. Additionally, N. coriiceps was exposed to 2.3 ± 0.3 mg of O₂ L^-1 for 12 h, and red-blooded Gobionotothen gibberifrons was exposed to both levels of hypoxia. Levels of HIF-1α were quantified in nuclei isolated from heart ventricles using western blotting. Transcript levels of genes involved in anaerobic metabolism, and known to be regulated by HIF-1, were quantified by real-time PCR, and lactate levels were measured in heart ventricles. Protein levels of HIF-1α increase in nuclei of hearts of N. coriiceps and C. aceratus in response to exposure to CT_MAX and in hearts of N. coriiceps exposed to severe hypoxia, yet mRNA levels of anaerobic metabolic genes do not increase in any species, nor do lactate levels increase, suggesting that HIF-1 does not stimulate metabolic remodeling in hearts of notothenioids under these conditions. Together, these data suggest that Antarctic notothenioids may be vulnerable to hypoxic events, which are likely to increase with climate warming.

Single and combined effects of the "Deadly trio" hypoxia, hypercapnia and warming on the cellular metabolism of the great scallop Pecten maximus

In the ocean the main climate drivers affecting marine organisms are warming, hypercapnia, and hypoxia. We investigated the acute effects of warming (W), warming plus hypercapnia (WHc, ~1800 μatm CO₂), warming plus hypoxia (WHo, ~12.1 kPa O₂), and a combined exposure of all three drivers (Deadly Trio, DT) on king scallops (Pecten maximus). All exposures started at 14 °C and temperature was increased by 2 °C once every 48 h until the lethal temperature was reached (28 °C). Gill samples were taken at 14 °C, 18 °C, 22 °C, and 26 °C and analyzed for their metabolic response by ¹H-nuclear magnetic resonance (NMR) spectroscopy. Scallops were most tolerant to WHc and most susceptible to oxygen reduction (WHo and DT). In particular under DT, scallops' mitochondrial energy metabolism was affected. Changes became apparent at 22 °C and 26 °C involving significant accumulation of glycogenic amino acids (e.g. glycine and valine) and anaerobic end-products (e.g. acetic acid and succinate). In line with these observations the LT₅₀ was lower under the exposure to DT (22.5 °C) than to W alone (~ 25 °C) indicating a narrowing of the thermal niche due to an imbalance between oxygen demand and supply.

Metabolomics Provide Sensitive Insights into the Impacts of Low Level Environmental Contamination on Fish Health-A Pilot Study

This exploratory study aims to investigate the health of sand flathead (Platycephalus bassensis) sampled from five sites in Port Phillip Bay, Australia using gas chromatography-mass spectrometry (GC-MS) metabolomics approaches. Three of the sites were the recipients of industrial, agricultural, and urban run-off and were considered urban sites, while the remaining two sites were remote from contaminant inputs, and hence classed as rural sites. Morphological parameters as well as polar and free fatty acid metabolites were used to investigate inter-site differences in fish health. Significant differences in liver somatic index (LSI) and metabolite abundance were observed between the urban and rural sites. Differences included higher LSI, an increased abundance of amino acids and energy metabolites, and reduced abundance of free fatty acids at the urban sites compared to the rural sites. These differences might be related to the additional energy requirements needed to cope with low-level contaminant exposure through energy demanding processes such as detoxification and antioxidant responses as well as differences in diet between the sites. In this study, we demonstrate that metabolomics approaches can offer a greater level of sensitivity compared to traditional parameters such as physiological parameters or biochemical markers of fish health, most of which showed no or little inter-site differences in the present study. Moreover, the metabolite responses are more informative than traditional biomarkers in terms of biological significance as disturbances in specific metabolic pathways can be identified.

The impact of acute thermal stress on the metabolome of the black rockfish (Sebastes schlegelii)

Acute change in water temperature causes heavy economic losses in the aquaculture industry. The present study investigated the metabolic and molecular effects of acute thermal stress on black rockfish (Sebastes schlegelii). Gas chromatography time-of-flight mass spectrometry (GC-TOF-MS)-based metabolomics was used to investigate the global metabolic response of black rockfish at a high water temperature (27°C), low water temperature (5°C) and normal water temperature (16°C). Metabolites involved in energy metabolism and basic amino acids were significantly increased upon acute exposure to 27°C (P < 0.05), and no change in metabolite levels occurred in the low water temperature group. However, certain fatty acid levels were elevated after cold stress (P < 0.05), and this effect was not observed in the 27°C group, suggesting that acute high and low temperature exposures caused different physiological responses. Using quantitative real-time PCR, we analyzed the expression of ubiquitin (ub), hypoxia-inducible factor (hif), lactate dehydrogenase (ldh), and acetyl-CoA carboxylase (acac). Higher expression levels of ub, hif, and ldh (P < 0.05) were observed in the high water temperature group, but no changes in these expression levels occurred in the low water temperature group. Our findings provide a potential metabolic profile for black rockfish when exposed to acute temperature stress and provide some insights into host metabolic and molecular responses to thermal stress.

STC1 and PTHrP Modify Carbohydrate and Lipid Metabolism in Liver of a Teleost Fish

Stanniocalcin 1 (STC1) and parathyroid hormone-related protein (PTHrP) are calciotropic hormones in vertebrates. Here, a recently hypothesized metabolic role for these hormones is tested on European sea bass treated with: (i) teleost PTHrP(1-34), (ii) PTHrP(1-34) and anti-STC1 serum (pro-PTHrP groups), (iii) a PTHrP antagonist PTHrP(7-34) or (iv) PTHrP(7-34) and STC1 (pro-STC1 groups). Livers were analysed using untargeted metabolic profiling based on proton nuclear magnetic resonance (¹H-NMR) spectroscopy. Concentrations of branched-chain amino acid (BCAA), alanine, glutamine and glutamate increased in pro-STC1 groups suggesting their mobilization from the muscle to the liver for degradation and gluconeogenesis from alanine and glutamine. In addition, only STC1 treatment decreased the concentrations of succinate, fumarate and acetate, indicating slowing of the citric acid cycle. In the pro-PTHrP groups the concentrations of glucose, erythritol and lactate decreased, indicative of gluconeogenesis from lactate. Taurine, trimethylamine, trimethylamine N-oxide and carnitine changed in opposite directions in the pro-STC1 versus the pro-PTHrP groups, suggesting opposite effects, with STC1 stimulating lipogenesis and PTHrP activating lipolysis/β-oxidation of fatty acids. These findings suggest a role for STC1 and PTHrP related to strategic energy mechanisms that involve the production of glucose and safeguard of liver glycogen reserves for stressful situations.