Fasting enhances cold resistance in fish through stimulating lipid catabolism and autophagy

Short-term dietary teprenone improved thermal tolerance and mitigated liver damage caused by heat stress in juvenile largemouth bass (Micropterus salmoides)

Heat stress seriously threatens fish survival and health, demanding immediate attention. Teprenone is a gastric mucosal protective agent that can induce heat shock protein expression. This research investigated the effects of teprenone on largemouth bass (Micropterus salmoides) subjected to heat stress. Juvenile fish were assigned to different groups: group C (control group, 0 mg teprenone/kg diet), T0, T200, T400, and T800 (0, 200, 400, and 800 mg teprenone/kg diet, respectively), which were fed for 3 days, followed by a day without the diet. All groups except group C were subjected to acute heat stress (from 24 °C to 35 °C at 1 °C per hour and then maintained at 35 °C for 3 h). The results were as follows: The critical thermal maxima were significantly higher in the T200, T400, and T800 groups compared with the T0 group (P < 0.05). Heat stress caused severe damage to the tissue morphology of the liver, while teprenone significantly reduced this injury (P < 0.05). Serum cortisol concentration decreased gradually as teprenone concentration increased, and the lowest concentration was observed in the T800 group (P < 0.05). Compared with the T0 group, the serum activities of aspartate aminotransferase, alanine aminotransferase, and gamma-glutamyl transferase were significantly lower in the T200, T400, and T800 groups (P < 0.05). The liver activities of catalase, total superoxide dismutase, and peroxidase were significantly higher in the T200 group than in the T0 group (P < 0.05). Transcript levels of the heat shock proteins (hsp90, hsp70, hspa5, and hsf1) and caspase family (caspase3 and caspase9) in the liver of the T200 group were significantly higher than those of the T0 group (P < 0.05). Western blot results showed that HSP70 and HSPA5 in the liver were significantly upregulated in the T200 group compared with the T0 group (P < 0.05). In summary, dietary teprenone improved thermal tolerance, alleviated heat stress damage in the liver, enhanced antioxidant capacity, and upregulated heat shock proteins in juvenile largemouth bass. This study offers theoretical support for applying teprenone in aquaculture to reduce financial losses caused by abiotic factors.

Histology, fatty acid composition, antioxidant and glycolipid metabolism, and transcriptome analyses of the acute cold stress response in Phoxinus lagowskii

Water temperature is a crucial environmental factor that significantly affects the physiological and biochemical processes of fish. Due to the occurrence of cold events in aquaculture, it is imperative to investigate how fish respond to cold stress. This study aims to uncover the mechanisms responds to acute cold stress by conducting a comprehensive analysis of the histomorphology, glycolipid metabolic and antioxidant enzymes, fatty acid composition and transcriptome at three temperatures (16 °C, 10 °C and 4 °C) in Phoxinus lagowskii. Our results showed that cold stress not damaged muscle microstructure but caused autophagy (at 10 °C). In addition, serum glucose (Glu) and triglycerides (TG) increased during cold stress. The activities of reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), fructose phosphokinase (PFK), hexokinase (HK), pyruvate kinase (PK), and malondialdehyde (MDA) content in muscle were measured and analyzed. During cold stress, superoxide dismutase and catalase activities increased, reactive oxygen species content decreased. No significant difference in Glutathione peroxidase (GPx) activity, malondialdehyde and total cholesterol (T-CHO) contents among groups. Phosphokinase and pyruvate kinase activities decreased, and HK activity increased during cold stress. Our study resulted in the identification of a total of 25,400 genes, with 2524 genes showing differential expression across different temperature treatments. Furthermore, KEGG pathway indicated that some pathways upregulated during light cold stress (at 10 °C, including autophagy, and AMP-activated protein kinase (AMPK) signaling pathway. Additionally, circadian rhythm is among the most enriched pathways in genes up-regulated during severe cold stress (at 4 °C). Our findings offer valuable insights into how cold-water fish respond to cold stress.

The physiological response of oriental river prawn Macrobrachium nipponense to starvation-induced stress

Environmental stresses play critical roles in the physiology of crustaceans. Food deprivation is an important environmental factor and a regular occurrence in both natural aquatic habitats and artificial ponds. However, the underlying physiological response mechanisms to starvation-caused stress in crustaceans are yet to be established. In the present study, the hepatopancreas tissue of Macrobrachium nipponense was transcriptome analyzed and examined for starvation effects on oxidative stress, DNA damage, autophagy, and apoptosis across four fasting stages (0 (control group), 7, 14, and 21 days). These results indicated that a ROS-mediated regulatory mechanism is critical to the entire fasting process. At the initial stage of starvation (fasting 0 d ~ 7 d), ROS concentration increased gradually, activating antioxidant enzymes to protect the cellular machinery from the detrimental effects of oxidative stress triggered by starvation-induced stress. ROS content production (hydrogen peroxide and superoxide anion) then rose continuously with prolonged starvation (fasting 7 d ~ 14 d), reaching peak levels and resulting in autophagy in hepatopancreas cells. During the final stages of starvation (fasting 14 d ~ 21 d), excessive ROS induced DNA damage and cell apoptosis. Furthermore, autophagolysosomes and apoptosis body were further identified with transmission electron microscopy. These findings lay a foundation for further scrutiny of the molecular mechanisms combating starvation-generated stress in M. nipponense and provide fishermen with the theoretical guidance for adopting fasting strategies in M. nipponense aquaculture.

Characterization of three lamp genes from largemouth bass (Micropterus salmoides): molecular cloning, expression patterns, and their transcriptional levels in response to fast and refeeding strategy

Lysosomes-associated membrane proteins (LAMPs), a family of glycosylated proteins and major constituents of the lysosomal membranes, play a dominant role in various cellular processes, including phagocytosis, autophagy and immunity in mammals. However, their roles in aquatic species remain poorly known. In the present study, three lamp genes were cloned and characterized from Micropterus salmoides. Subsequently, their transcriptional levels in response to different nutritional status were investigated. The full-length coding sequences of lamp1, lamp2 and lamp3 were 1251bp, 1224bp and 771bp, encoding 416, 407 and 256 amino acids, respectively. Multiple sequence alignment showed that LAMP1-3 were highly conserved among the different fish species, respectively. 3-D structure prediction, genomic survey, and phylogenetic analysis were further confirmed that these genes are widely existed in vertebrates. The mRNA expression of the three genes was ubiquitously expressed in all selected tissues, including liver, brain, gill, heart, muscle, spleen, kidney, stomach, adipose and intestine, lamp1 shows highly transcript levels in brain and muscle, lamp2 displays highly expression level in heart, muscle and spleen, but lamp3 shows highly transcript level in spleen, liver and kidney. To analyze the function of the three genes under starvation stress in largemouth bass, three experimental treatment groups (fasted group and refeeding group, control group) were established in the current study. The results indicated that the expression of lamp1 was significant induced after starvation, and then returned to normal levels after refeeding in the liver. The expression of lamp2 and lamp3 exhibited the same trend in the liver. In addition, in the spleen and the kidney, the transcript level of lamp1 and lamp2 was remarkably increased in the fasted treatment group and slightly decreased in the refed treatment group, respectively. Collectively, our findings suggest that three lamp genes may have differential function in the immune and energetic organism in largemouth bass, which is helpful in understanding roles of lamps in aquatic species.

The preferential utilization of hepatic glycogen as energy substrates in largemouth bass (Micropterus salmoides) under short-term starvation

To elucidate the underlying mechanism of the energy metabolism in largemouth bass (Micropterus salmoides), cultured fish (initial body weight: 77.57 ± 0.75 g) in the present study were starved for 0 h, 12 h, 24 h, 48 h, 96 h and 192 h, respectively. The proximate composition analysis showed that short-term starvation induced a significant up-regulation in crude protein proportion in hepatic of cultured fish (P < 0.05). However, short-term starvation significantly decreased the hepatosomatic index and the viscerosomatic index of cultured fish (P < 0.05). The exact hepatic glycogen content in the group starved for 92 h presented remarkable decrease (P < 0.05). Meanwhile, compared with the weight change of lipid and protein (mg) in hepatic (y = 0.0007x2 - 0.2827x + 49.402; y = 0.0013x2 - 0.5666x + 165.31), the decreasing trend of weight in glycogen (mg) was more pronounced (y = 0.0032x2 - 1.817x + 326.52), which suggested the preferential utilization of hepatic glycogen as energy substrates under short-term starvation. Gene expression analysis revealed that the starvation down-regulated the expression of insulin-like growth factor 1 and genes of TOR pathway, such as target of rapamycin (tor) and ribosomal protein S6 (s6) (P < 0.05). In addition, the starvation significantly enhanced expression of lipolysis-related genes, including hormone-sensitive lipase (hsl) and carnitine palmitoyl transferase I (cpt1), but down-regulated lipogenesis as indicated by the inhibited expression of fatty acids synthase (fas), acetyl-CoA carboxylase 1 (acc1) and acetyl-CoA carboxylase 2 (acc2) (P < 0.05). Starvation of 24 h up-regulated the expression of glycolysis genes, glucokinase (gk), phosphofructokinase liver type (pfkl) and pyruvate kinase (pk), and then their expression returned to the normal level. Meanwhile, the expression of gluconeogenesis genes, such as glucose-6-phosphatase catalytic subunit (g6pc), fructose-1,6-bisphosphatase-1 (fbp1) and phosphoenolpyruvate carboxy kinase (pepck), was significantly inhibited with the short-term starvation (P < 0.05). In conclusion, short-term starvation induced an overall decline in growth performance, but it could deplete the hepatic glycogen accumulation and mobilize glycogen for energy effectively.

Zebrafish Feed Intake: A Systematic Review for Standardizing Feeding Management in Laboratory Conditions

Zebrafish are one of the most used animal models in biological research and a cost-effective alternative to rodents. Despite this, nutritional requirements and standardized feeding protocols have not yet been established for this species. This is important to avoid nutritional effects on experimental outcomes, and especially when zebrafish models are used in preclinical studies, as many diseases have nutritional confounding factors. A key aspect of zebrafish nutrition is related to feed intake, the amount of feed ingested by each fish daily. With the goal of standardizing feeding protocols among the zebrafish community, this paper systematically reviews the available data from 73 studies on zebrafish feed intake, feeding regimes (levels), and diet composition. Great variability was observed regarding diet composition, especially regarding crude protein (mean 44.98 ± 9.87%) and lipid content (9.91 ± 5.40%). Interestingly, the gross energy levels of the zebrafish diets were similar across the reviewed studies (20.39 ± 2.10 kilojoules/g of feed). In most of the reviewed papers, fish received a predetermined quantity of feed (feed supplied). The authors fed the fish according to the voluntary intake and then calculated feed intake (FI) in only 17 papers. From a quantitative point of view, FI was higher than when a fixed quantity (pre-defined) of feed was supplied. Also, the literature showed that many biotic and abiotic factors may affect zebrafish FI. Finally, based on the FI data gathered from the literature, a new feeding protocol is proposed. In summary, a daily feeding rate of 9-10% of body weight is proposed for larvae, whereas these values are equal to 6-8% for juveniles and 5% for adults when a dry feed with a proper protein and energy content is used.

Temperature-Dependent Relationship of Autophagy and Apoptotic Signaling During Cold-Water Immersion in Young and Older Males

Autophagy is a crucial cytoprotective mechanism preventing the accumulation of cellular damage, especially during external stimuli such as cold exposure. Older adults poorly tolerate cold exposure and age-related impairments in autophagy may contribute to the associated reductions in cold tolerance. The purpose of this investigation is to evaluate the effect of different intensities of in vivo cold-water immersion and in vitro cold exposure on autophagic and apoptotic signaling in young and older males. Peripheral blood mononuclear cells (PBMCs) are isolated at baseline, end-cold exposure, and after 3 h of thermoneutral recovery. Additionally, PBMCs are treated with rapamycin and bafilomycin prior to in vitro cold exposure equivalent to in vivo core temperatures (35-37 °C). Proteins associated with autophagy, apoptosis, the heat shock response, and inflammation are analyzed via Western blotting. Moderate cold stress (0.5 °C decrease in core temperature) increased autophagic and heat shock protein activity while high cold stress (1.0 °C decrease in core temperature) augmented apoptosis in young males. In older males, minimal autophagic activation during both cold-water exposures are associated with increased apoptotic and inflammatory proteins. Although in vitro cold exposure confirmed age-related dysfunction in autophagy, rapamycin-induced stimulation of autophagic proteins underlie the potential to reverse age-related vulnerability to cold exposure.

Effects of intermittent cold stimulation on growth performance, meat quality, antioxidant capacity and liver lipid metabolism in broiler chickens

Intermittent cold stimulation (ICS) enhances broilers' resistance to cold stress. Nonetheless, further research is needed to investigate the underlying mechanisms that enhance cold stress resistance. A total of 160 one-day-old male Ross 308 broilers were randomly divided into 2 groups (CC and CS5), with the CC group managing temperature according to the standard for broiler growth stages, while the CS5 group were subjected to cold stimulation at a temperature 3℃ lower than the CC group for 5 h, every 2 d from 15 to 35 d. Sampling was conducted at 36 d (36D), 50 d (50D) and after acute cold stress for 24 h (Y24). First, we examined the effects of ICS on broiler growth performance, meat quality, antioxidant capacity, and lipid metabolism. The results demonstrated that ICS enhanced the performance of broilers to a certain degree. Specifically, the average weight gain in the CS5 group was significantly higher than that of the CC group, and the feed conversion ratio significantly decreased compared to CC at 4 W and 6 W (P ≤ 0.05). Compared with the CC group, cold stimulation significantly reduced drip loss, shearing force, and yellowness (a* value) of chicken meat, while significantly increased redness (b* value) (P ≤ 0.05). At Y24, the levels of T-AOC and GSH-PX in the serum of the CS5 group were significantly higher than those of the CC group, while the level of MDA was significantly lower (P ≤ 0.05). The content of TG, FFA, and VLDL in the serum of the CS5 group was significantly elevated, whereas the level of TC and HDL was significantly lower (P ≤ 0.05). In addition, we further explored whether AMPK-mTOR pathway is involved in the regulation of changes in lipid metabolism and the possible regulatory mechanisms downstream of the signaling pathway. The results showed that ICS significantly upregulated the expression levels of AMPK mRNA and protein in the liver of the CS5 group at 36D and Y24, while significantly down-regulating mTOR (P ≤ 0.05). Compared with the CC group, ICS significantly down-regulated the mRNA expression levels of lipid synthesis and endoplasmic reticulum stress-related genes (SREBP1c, FAS, SCD, ACC, GRP78 and PERK) at 36D and Y24, while significantly up-regulating the mRNA expression levels of lipid decomposition and autophagy-related genes (PPAR and LC3) (P ≤ 0.05). In addition, at Y24, the protein expression levels of endoplasmic reticulum stress-related genes (GRP78) in the CS5 group were significantly lower, while autophagy-related genes (LC3 and ATG7) were significantly higher (P ≤ 0.05). ICS can affect meat quality and lipid metabolism in broilers, and when broilers are subjected to acute cold stress, broilers trained with cold stimulation have stronger lipid metabolism capacity.

Mitigation of cold stress in Nile tilapia (Oreochromis niloticus) through dietary lipids supplementation: a preliminary network meta-analysis

There is a growing body of evidence suggesting that water temperature can significantly impact the dietary fatty acid requirements of Nile tilapia (Oreochromis niloticus). Therefore, this study assessed the effectiveness of different dietary lipid sources on the growth performance of Nile tilapia reared at suboptimal temperatures. A network meta-analysis was performed, including searches of PubMed and Scopus from inception to January 2022, for trials that evaluated the effects of lipid sources on cold-stressed Nile tilapia. The Bayesian hierarchical framework was used to pool and compare the effect sizes of growth parameters such as weight gain, feed intake, and feed conversion ratio (FCR). Furthermore, the surface under the cumulative ranking curve (SUCRA) was obtained to calculate the probability that each lipid source was the most effective against cold stress. All subsequent numbers refer to comparisons with diets containing only fish oil. Dietary Aurantiochytrium significantly increased weight gain (SMD = 2.00, CrI: 0.70 to 3.40). In contrast, diets containing coconut oil led to significantly lower weight gain (SMD = - 3.30, CrI: - 6.00 to - 0.63) and higher FCR (SMD = 17.0, CrI: 6.70 to 27.0). Additionally, dietary corn oil was associated with a decrease in feed intake (SMD = - 2.32, CrI: - 3.91 to - 0.80), while a combination of fish and corn oil reduced FCR (SMD = - 5.70, CrI: - 11.0 to - 0.81). In general, the analysis of SUCRA values revealed that in cold-stressed Nile tilapia, Aurantiochytrium, sunflower oil, and the combination of fish and corn oil were the most effective lipid sources for improving growth at suboptimal temperatures. The results of the current study can serve as a basis for future studies that focus on the use of dietary lipid sources to mitigate cold stress in Nile tilapia.

Differential modulation of digestive enzymes and energy reserves at different times after feeding in juveniles of the marine estuarine-dependent flatfish Paralichthys orbignyanus (Valenciennes, 1839)

Integrative studies are lacking on the responses of digestive enzymes and energy reserves in conjunction with morphological traits at distinct postprandial times in marine estuarine-dependent flatfishes of ecological and economic importance, such as Paralichthys orbignyanus. We determined total weight (TW), hepato-somatic index (IH), activities of digestive enzymes in the intestine, and the concentration of energy reserves in the liver and the muscle at 0, 24, 72, and 360 h after feeding in juveniles of P. orbignyanus. Amylase activity decreased at 72 h (about 30%). Maltase, sucrose, and lipase activities reached peak at 24 h (67%, 600%, and 35%, respectively). Trypsin and aminopeptidase-N activities at 24 and 72 h, respectively, were lower than those at t = 0 (53% and 30%). A peak increase in the concentration of glycogen and triglycerides in the liver (24 h) (86% and 89%, respectively) occurred. In muscle, glycogen and triglyceride concentrations were unchanged at 24 h and higher at 72 and 360 h (100% and 60%). No changes were found in TW, IH, free glucose in the liver and muscle, and protein in the liver. The protein concentration in the muscle sharply increased at 24 and 360 h after feeding (60%). The results indicate a distinct and specific response of central components of carbohydrate, lipid, and protein metabolism that could be adjustments at the biochemical level upon periods of irregular feeding and even of long-term food deprivation inside coastal lagoons or estuaries. The distinct responses of digestive enzymes in the intestine and energy reserves in the liver and muscle suggest the differential modulation of tissue-specific anabolic and catabolic pathways that would allow the maintenance of physical conditions.

Inhibition of mitochondrial fatty acid β-oxidation activates mTORC1 pathway and protein synthesis via Gcn5-dependent acetylation of Raptor in zebrafish

Pharmacological inhibition of mitochondrial fatty acid oxidation (FAO) has been clinically used to alleviate certain metabolic diseases by remodeling cellular metabolism. However, mitochondrial FAO inhibition also leads to mechanistic target of rapamycin complex 1 (mTORC1) activation-related protein synthesis and tissue hypertrophy, but the mechanism remains unclear. Here, by using a mitochondrial FAO inhibitor (mildronate or etomoxir) or knocking out carnitine palmitoyltransferase-1, we revealed that mitochondrial FAO inhibition activated the mTORC1 pathway through general control nondepressible 5-dependent Raptor acetylation. Mitochondrial FAO inhibition significantly promoted glucose catabolism and increased intracellular acetyl-CoA levels. In response to the increased intracellular acetyl-CoA, acetyltransferase general control nondepressible 5 activated mTORC1 by catalyzing Raptor acetylation through direct interaction. Further investigation also screened Raptor deacetylase histone deacetylase class II and identified histone deacetylase 7 as a potential regulator of Raptor. These results provide a possible mechanistic explanation for the mTORC1 activation after mitochondrial FAO inhibition and also bring light to reveal the roles of nutrient metabolic remodeling in regulating protein acetylation by affecting acetyl-CoA production.

Hypoxia tolerance in fish depends on catabolic preference between lipids and carbohydrates

Hypoxia is a common environmental stress factor in aquatic organisms, which varies among fish species. However, the mechanisms underlying the ability of fish species to tolerate hypoxia are not well known. Here, we showed that hypoxia response in different fish species was affected by lipid catabolism and preference for lipid or carbohydrate energy sources. Activation of biochemical lipid catabolism through peroxisome proliferator-activated receptor alpha (Pparα) or increasing mitochondrial fat oxidation in tilapia decreased tolerance to acute hypoxia by increasing oxygen consumption and oxidative damage and reducing carbohydrate catabolism as an energy source. Conversely, lipid catabolism inhibition by suppressing entry of lipids into mitochondria in tilapia or individually knocking out three key genes of lipid catabolism in zebrafish increased tolerance to acute hypoxia by decreasing oxygen consumption and oxidative damage and promoting carbohydrate catabolism. However, anaerobic glycolysis suppression eliminated lipid catabolism inhibition-promoted hypoxia tolerance in adipose triglyceride lipase (atgl) mutant zebrafish. Using 14 fish species with different trophic levels and taxonomic status, the fish preferentially using lipids for energy were more intolerant to acute hypoxia than those preferentially using carbohydrates. Our study shows that hypoxia tolerance in fish depends on catabolic preference for lipids or carbohydrates, which can be modified by regulating lipid catabolism.

Dietary restriction to optimize T cell immunity is an ancient survival strategy conserved in vertebrate evolution

Recent advances highlight a key role of transient fasting in optimizing immunity of human and mouse. However, it remains unknown whether this strategy is independently acquired by mammals during evolution or instead represents gradually evolved functions common to vertebrates. Using a tilapia model, we report that T cells are the main executors of the response of the immune system to fasting and that dietary restriction bidirectionally modulates T cell immunity. Long-term fasting impaired T cell immunity by inducing intense autophagy, apoptosis, and aberrant inflammation. However, transient dietary restriction triggered moderate autophagy to optimize T cell response by maintaining homeostasis, alleviating inflammation and tissue damage, as well as enhancing T cell activation, proliferation and function. Furthermore, AMPK is the central hub linking fasting and autophagy-controlled T cell immunity in tilapia. Our findings demonstrate that dietary restriction to optimize immunity is an ancient strategy conserved in vertebrate evolution, providing novel perspectives for understanding the adaptive evolution of T cell response.

In Vivo Tracking of Persistent Organic Pollutants via a Coaxially Integrated and Implanted Photofuel Microsensor

In vivo tracking of persistent organic pollutants (POPs) is of great significance for assessing their risks to the ecological environment and human health. However, existing in vivo POPs detection methods are limited by the lethal sampling of living organisms, complex sample preparation processes, or bulky testing equipment. Photoelectrochemical (PEC) sensing with the merits of high sensitivity and simple equipment is a fast-developed method for in vivo analysis. A major obstacle for in vivo PEC sensors is the separated implantation of multiple electrodes and a light source, which raises concerns like multielectrode biofouling and electroactive molecules interference in the complex environment, uncertain electrode implant distance, and multiple insertion operations. Here, a coaxially implanted photofuel microsensor was developed by hiding the optical fiber-based photoanode inside the glass capillary-based biocathode, and the model target PCB77 can be detected with an ultralow detection limit (2.8 fg/mL). This unique photoanode-biocathode-light source integrated structure ensures excellent selectivity, good antifouling ability and biocompatibility, high accuracy, and less implant mechanical damage. Combined with a handheld pH meter, our sensor achieved convenient and direct tracking of the bioaccumulation levels of PCB77 in freely swimming fish.

Metabolic adaptation to high-starch diet in largemouth bass (Micropterus salmoides) was associated with the restoration of metabolic functions via inflammation, bile acid synthesis and energy metabolism

A short-term 2-week (2w) and long-term 8-week (8w) feeding trial was conducted to investigate the effects of low-starch (LS) and high-starch (HS) diets on the growth performance, metabolism and liver health of largemouth bass (Micropterus salmoides). Two isonitrogenous and isolipidic diets containing two levels of starch (LS, 9·06 %; HS, 13·56 %) were fed to largemouth bass. The results indicated that HS diet had no significant effects on specific growth rate during 2w, whereas significantly lowered specific growth rate at 8w. HS diet significantly increased hepatic glycolysis and gluconeogenesis at postprandial 24 h in 2w. The hepatosomatic index, plasma alkaline phosphatase, total bile acid (TBA) levels, and hepatic glycogen, TAG, total cholesterol, TBA, and NEFA contents were significantly increased in the HS group at 2w. Moreover, HS diet up-regulated fatty acid and TAG synthesis-related genes and down-regulated TAG hydrolysis and β-oxidation-related genes. Therefore, the glucolipid metabolism disorders resulted in metabolic liver disease induced by HS diet at 2w. However, the up-regulation of bile acid synthesis, inflammation and energy metabolism-related genes in 2w indicated that largemouth bass was still in a state of 'self-repair' response. Interestingly, all the metabolic parameters were returned to homoeostasis, with up-regulation of intestinal glucose uptake and transport-related genes, even hepatic histopathological analysis showed no obvious abnormality in the HS group in 8w. In conclusion, HS feed induced short-term acute metabolic disorder, but long-term metabolic adaptation to HS diet was related to repairing metabolism disorders via improving inflammatory responses, bile acid synthesis and energy metabolism. These results strongly indicated that the largemouth bass owned certain adaptability to HS diet.

Red porgy's (Pagrus pagrus) cellular physiology and antioxidant defense in response to seasonality

Physiological stress patterns of marine organisms in their natural habitats are considerably complex in space and time. These patterns can eventually contribute in the shaping of fish' thermal limits under natural conditions. In the view of the knowledge gap regarding red porgy's thermal physiology, in combination with the characterization of the Mediterranean Sea as a climate change ''hotspot'', the aim of the present study was to investigate this species biochemical responses to constantly changing field conditions. To achieve this goal, Heat Shock Response (HSR), MAPKs pathway, autophagy, apoptosis, lipid peroxidation and antioxidant defense were estimated and exhibited a seasonal pattern. In general, all the examined biochemical indicators expressed high levels parallel to the increasing seawater temperature in spring, although several bio-indicators have shown increased levels when fish were cold-acclimatized. Similar to other sparids, the observed patterns of physiological responses in red porgy may support the concept of eurythermy.

High cholesterol intake remodels cholesterol turnover and energy homeostasis in Nile tilapia (Oreochromis niloticus)

The roles of dietary cholesterol in fish physiology are currently contradictory. The issue reflects the limited studies on the metabolic consequences of cholesterol intake in fish. The present study investigated the metabolic responses to high cholesterol intake in Nile tilapia (Oreochromis niloticus), which were fed with four cholesterol-contained diets (0.8, 1.6, 2.4 and 3.2%) and a control diet for eight weeks. All fish-fed cholesterol diets showed increased body weight, but accumulated cholesterol (the peak level was in the 1.6% cholesterol group). Then, we selected 1.6% cholesterol and control diets for further analysis. The high cholesterol diet impaired liver function and reduced mitochondria number in fish. Furthermore, high cholesterol intake triggered protective adaptation via (1) inhibiting endogenous cholesterol synthesis, (2) elevating the expression of genes related to cholesterol esterification and efflux, and (3) promoting chenodeoxycholic acid synthesis and efflux. Accordingly, high cholesterol intake reshaped the fish gut microbiome by increasing the abundance of Lactobacillus spp. and Mycobacterium spp., both of which are involved in cholesterol and/or bile acids catabolism. Moreover, high cholesterol intake inhibited lipid catabolic activities through mitochondrial β-oxidation, and lysosome-mediated lipophagy, and depressed insulin signaling sensitivity. Protein catabolism was elevated as a compulsory response to maintain energy homeostasis. Therefore, although high cholesterol intake promoted growth, it led to metabolic disorders in fish. For the first time, this study provides evidence for the systemic metabolic response to high cholesterol intake in fish. This knowledge contributes to an understanding of the metabolic syndromes caused by high cholesterol intake or deposition in fish.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42995-022-00158-7.

Effects of temperature and combinational exposures on lipid metabolism in aquatic invertebrates

Studies of changes in fatty acids in response to environmental temperature changes have been conducted in many species, particularly mammals. However, few studies have considered aquatic invertebrates, even though they are particularly vulnerable to changes in environmental temperature. In this review, we summarize the process by which animals synthesize common fatty acids and point out differences between the fatty acid profiles of vertebrates and those of aquatic invertebrates. Unlike vertebrates, some aquatic invertebrates can directly synthesize polyunsaturated fatty acids (PUFAs), which can be used to respond to temperature changes. Various studies have shown that aquatic invertebrates increase the degree of saturation in their fatty acids through an increase in saturated fatty acid production or a decrease in PUFAs as the temperature increases. In addition, we summarize recent studies that have examined the complex effects of temperature and combinational stressors to determine whether the degree of saturation in aquatic invertebrates is influenced by other factors. The combined effects of carbon dioxide partial pressure, food quality, starvation, salinity, and chemical exposures have been confirmed, and fatty acid profile changes in response to high temperature were greater than those from combinational stressors.

The divergent effects of moderate climate warming on the gut microbiota and energetic state of cold-climate lizards from open and semi-closed microhabitats

INTRODUCTION

Understanding the physiological responses to warming temperatures is critical for evaluating the vulnerabilities of animals to climate warming. The physiological responses are increasingly affected by gut microbiota. However, the interactions between physiological responses and the gut microbiota of sympatric animals from various microhabitats in the face of climate change remain largely unknown.

METHODS

To evaluate the effects of warming temperatures on animals from different microhabitats, we compared locomotor performance, metabolic rate, growth, survival, and gut microbiota of two sympatric ectothermic species (Eremias argus and Takydromus amurensis) from open and semi-closed microhabitats under present and moderate warming climate conditions, respectively.

RESULTS AND DISCUSSION

We found that locomotor performance and growth rates of snout-vent length (SVL) were enhanced in both lizard species by warming climate. Interestingly, warming temperatures enhanced resting metabolic rates (RMR) in the open-habitat lizard, E. argus, but depressed them in the semi-closed habitat lizard, T. amurensis. Reversely, the metabolism-related gut microbiota was not affected by warming in E. argus, whereas it was significantly enhanced by warming in T. amurensis, indicating a plausible compensatory effect of the gut microbiota on the metabolic regulation of T. amurensis. Furthermore, warming likely improved immunity in both lizard species by significantly reducing pathogenic bacteria while increasing probiotics. This study found that high-latitude sympatric lizards from both open and semi-closed habitats were beneficial to warming temperatures by physiological modification and regulation of the gut microbiota and highlighted the importance of integrating the physiology and gut microbiota in evaluating the vulnerability of animals to climate warming.

An Integrated Bioinformatics Approach to Identify Network-Derived Hub Genes in Starving Zebrafish

The present study was aimed at identifying causative hub genes within modules formed by co-expression and protein-protein interaction (PPI) networks, followed by Bayesian network (BN) construction in the liver transcriptome of starved zebrafish. To this end, the GSE11107 and GSE112272 datasets from the GEO databases were downloaded and meta-analyzed using the MetaDE package, an add-on R package. Differentially expressed genes (DEGs) were identified based upon expression intensity N(µ = 0.2, σ² = 0.4). Reconstruction of BNs was performed by the bnlearn R package on genes within modules using STRINGdb and CEMiTool. ndufs5 (shared among PPI, BN and COEX), rps26, rpl10, sdhc (shared between PPI and BN), ndufa6, ndufa10, ndufb8 (shared between PPI and COEX), skp1, atp5h, ndufb10, rpl5b, zgc:193613, zgc:123327, zgc:123178, wu:fc58f10, zgc:111986, wu:fc37b12, taldo1, wu:fb62f08, zgc:64133 and acp5a (shared between COEX and BN) were identified as causative hub genes affecting gene expression in the liver of starving zebrafish. Future work will shed light on using integrative analyses of miRNA and DNA microarrays simultaneously, and performing in silico and experimental validation of these hub-causative (CST) genes affecting starvation in zebrafish.

Understanding the Function and Mechanism of Zebrafish Tmem39b in Regulating Cold Resistance

Autophagy and endoplasmic reticulum (ER) stress response are among the key pathways regulating cold resistance of fish through eliminating damaged cellular components and facilitating the restoration of cell homeostasis upon exposure to acute cold stress. The transmembrane protein 39A (TMEM39A) was reported to regulate both autophagy and ER stress response, but its vertebrate-specific paralog, the transmembrane protein 39B (TMEM39B), has not been characterized. In the current study, we generate tmem39b-knockout zebrafish lines and characterize their survival ability under acute cold stress. We observed that the dysfunction of Tmem39b remarkably decreased the cold resilience of both the larval and adult zebrafish. Gene transcription in the larvae exposed to cold stress and rewarming were characterized by RNA sequencing (RNA-seq) to explore the mechanisms underlying functions of Tmem39b in regulating cold resistance. The results indicate that the deficiency of Tmem39b attenuates the up-regulation of both cold- and rewarming-induced genes. The cold-induced transcription factor genes bif1.2, fosab, and egr1, and the rewarming-activated immune genes c3a.3, il11a, and sting1 are the representatives influenced by Tmem39b dysfunction. However, the loss of tmem39b has little effect on the transcription of the ER stress response- and autophagy-related genes. The measurements of the phosphorylated H2A histone family member X (at Ser 139, abbreviated as γH2AX) demonstrate that zebrafish Tmem39b protects the cells against DNA damage caused by exposure to the cold-warming stress and facilitates tissue damage repair during the recovery phase. The gene modules underlying the functions of Tmem39b in zebrafish are highly enriched in biological processes associated with immune response. The dysfunction of Tmem39b also attenuates the up-regulation of tissue C-reactive protein (CRP) content upon rewarming. Together, our data shed new light on the function and mechanism of Tmem39b in regulating the cold resistance of fish.

Involvement of Mechanistic Target of Rapamycin (mTOR) in Valine Orexigenic Effects in Rainbow Trout

This study was aimed at clarifying the importance of a mechanistic target of rapamycin (mTOR) in the central orexigenic effect of valine in fish. For this, rainbow trout (Oncorhynchus mykiss) were intracerebroventricularly (ICV) injected with valine alone or in the presence of rapamycin as the mTOR inhibitor, and two experiments were performed. In the first experiment, we evaluated feed intake levels. In the second experiment, we evaluated in the hypothalamus and telencephalon the following: (1) the phosphorylation status of mTOR and its downstream effectors ribosomal protein S6 and p70 S6 kinase 1 (S6K1), (2) the abundance and phosphorylation status of transcription factors involved in appetite regulation, and (3) the mRNA levels of key neuropeptides associated with homeostatic regulation of feed intake in fish. Rising central levels of valine clearly resulted in an orexigenic response in rainbow trout. This response occurred in parallel with mTOR activation in both the hypothalamus and telencephalon, as supported by depressant changes in proteins involved in mTOR signalling (S6 and S6K1). Also, these changes disappeared in the presence of rapamycin. However, it is not clear which precise mechanisms link the activation of mTOR and the alteration in feed intake levels since we did not observe changes in mRNA levels of appetite-regulatory neuropeptides as well as in the phosphorylation status and levels of integrative proteins.

Mild cold stress specifically disturbs clustering movement of DFCs and sequential organ left-right patterning in zebrafish

In poikilothermic animals, the distinct acclimatization ability of different organs has been previously addressed, while the tissue-specific role of cold stress in early development is largely unknown. In this study, we discovered that despite its role in delaying embryonic development, mild cold stress (22°C) does not disturb multiple-organ progenitor specification, but does give rise to organ left-right (LR) patterning defects. Regarding the mechanism, the data showed that mild cold stress downregulated the expression of cell-adhesion genes cdh1 and cdh2 during gastrulation, especially in dorsal forerunner cells (DFCs), which partially disturbed the clustering movement of DFCs, Kupffer’s vesicle (KV) morphogenesis, and ciliogenesis. As a result, the defects of KV/cilia disrupted asymmetric nodal signaling and subsequent heart and liver LR patterning. In conclusion, our data novelly identified that, in early development, DFCs are more sensitive to mild cold stress, and mild cold stress repressed the expression of cell adhesion-related gene cdh1 and cdh2. This role partially disturbed the clustering movement of DFCs, which resulted in defective KV/cilia development and sequential organ LR patterning defects.

Exposure of zebrafish to a cold environment triggered cellular autophagy in zebrafish liver

Water temperature is the major ecophysiological factor for fish survival in nature and aquaculture. Compared with many homeotherms, fish can survive prolonged periods under the condition of low temperature. However, the metabolic strategies of the liver under a cold environment are still unknown in this species. In our present study, adult zebrafish were exposed to a cold or cold plus starvation environment to analyse the morphological characteristics of hepatocytes by light microscopy and transmission electron microscopy (TEM). The fish livers were dissected and observed under a microscope, and the liver size and shape appeared normal in all groups. Periodic acid-Schiff and TEM analysis showed that hepatic glycogen was significantly lower in zebrafish exposed to cold acclimation (CF group) than that zebrafish at the control water temperature (CT group). Moreover, qPCR and IHC results indicated that the expression of PYGL (a key enzyme involved in glycogenolysis) markedly increased in the CF group. After cold plus starvation treatment (CS group), autophagy activity was significantly enhanced and numerous mitophagic vacuoles were present in the cytoplasm of hepatocytes. In conclusion, hepatic glycogen was first mobilizing to supply energy, and then autophagy, especially mitophagy, played vital roles during nutrient deprivation in fish species.

Prejuveniles of Mugil liza (Actinopterygii; Fam. Mugilidae) show digestive and metabolic flexibility upon different postprandial times and refeeding

Many animals face periods of feeding restrictions implying fasting and refeeding. The determination of digestive/metabolic and body condition parameters at different times of food deprivation and after refeeding allows to evaluate the postprandial dynamics, the transition from feeding to fasting and the capacity to reverse digestive and metabolic alterations. In spite of its physiological importance, studies on estuarine-dependent detritivore fish are lacking. We determined total mass (TM), relative intestine length (RIL), hepatosomatic index (HSI), digestive enzymes activities in the intestine and energy reserves in liver and muscle at 0, 24, 72, 144 and 240 h after feeding and at 72 h after refeeding in prejuveniles of Mugil liza (Mugilidae) as a model species. After feeding, a decrease occurred in: TM (144 h, 25%), RIL (144 h, 23%); amylase and maltase (72 h, 45 and 35%), sucrase (24 h, 40%) and lipase (24 h, 70%) in intestine; glycogen and free glucose (72 h, 90 and 92%) in liver. In muscle, glycogen (72-144 h) and free glucose (144 h) (170% and 165%, respectively) peak increased; triglycerides decreased at 24-240 h (50%). After refeeding TM, RIL, carbohydrases activities in intestine, glycogen and free glucose in liver were recovered. In muscle, glycogen and free glucose were similar to 0 h; lipase activity and triglycerides were not recovered. Trypsin and APN in intestine, triglycerides in liver, protein in liver and muscle and HSI did not change. The differential modulation of key components of carbohydrates and lipid metabolism after feeding/refeeding would allow to face fasting and recover body condition. Our results improve lacking knowledge about digestive and metabolic physiology of detritivore fish.

An updated review of cold shock and cold stress in fish

Temperature is critical in regulating virtually all biological functions in fish. Low temperature stress (cold shock/stress) is an often-overlooked challenge that many fish face as a result of both natural events and anthropogenic activities. In this study, we present an updated review of the cold shock literature based on a comprehensive literature search, following an initial review on the subject by M.R. Donaldson and colleagues, published in a 2008 volume of this journal. We focus on how knowledge on cold shock and fish has evolved over the past decade, describing advances in the understanding of the generalized stress response in fish under cold stress, what metrics may be used to quantify cold stress and what knowledge gaps remain to be addressed in future research. We also describe the relevance of cold shock as it pertains to environmental managers, policymakers and industry professionals, including practical applications of cold shock. Although substantial progress has been made in addressing some of the knowledge gaps identified a decade ago, other topics (e.g., population-level effects and interactions between primary, secondary and tertiary stress responses) have received little or no attention despite their significance to fish biology and thermal stress. Approaches using combinations of primary, secondary and tertiary stress responses are crucial as a research priority to better understand the mechanisms underlying cold shock responses, from short-term physiological changes to individual- and population-level effects, thereby providing researchers with better means of quantifying cold shock in laboratory and field settings.

Exploring Thermal Sensitivities and Adaptations of Oxidative Phosphorylation Pathways

Temperature shifts are a major challenge to animals; they drive adaptations in organisms and species, and affect all physiological functions in ectothermic organisms. Understanding the origin and mechanisms of these adaptations is critical for determining whether ectothermic organisms will be able to survive when faced with global climate change. Mitochondrial oxidative phosphorylation is thought to be an important metabolic player in this regard, since the capacity of the mitochondria to produce energy greatly varies according to temperature. However, organism survival and fitness depend not only on how much energy is produced, but, more precisely, on how oxidative phosphorylation is affected and which step of the process dictates thermal sensitivity. These questions need to be addressed from a new perspective involving a complex view of mitochondrial oxidative phosphorylation and its related pathways. In this review, we examine the effect of temperature on the commonly measured pathways, but mainly focus on the potential impact of lesser-studied pathways and related steps, including the electron-transferring flavoprotein pathway, glycerophosphate dehydrogenase, dihydroorotate dehydrogenase, choline dehydrogenase, proline dehydrogenase, and sulfide:quinone oxidoreductase. Our objective is to reveal new avenues of research that can address the impact of temperature on oxidative phosphorylation in all its complexity to better portray the limitations and the potential adaptations of aerobic metabolism.

Beneficial Effects of Warming Temperatures on Embryonic and Hatchling Development in a Low-Latitude Margin Population of the High-Latitude Lizard Lacerta agilis

The effects of warming temperatures on embryonic and hatchling development are critical for determining the vulnerability of species to climate warming. However, these effects have rarely been investigated in high-latitude oviparous species, particularly in their low-latitude margin populations. This study investigated the embryonic and hatchling development and fitness-related traits of a low-latitude margin population of a high-latitude lizard (Lacerta agilis). These traits were examined under present (24°C), moderate warming (27 and 30°C), and severe warming scenarios (33°C). Based on embryonic and hatchling responses to thermal variation, this study aimed to predict the vulnerability of the early life stages of low-latitude margin population of Lacerta agilis to climate warming. The incubation period of the low-latitude margin population of Lacerta agilis decreased as the temperature increased from 24 to 33°C. Hatching success was similar at 24, 27, and 30°C but decreased significantly at 33°C. No differences with temperature were observed for hatchling snout-vent length and hatchling body mass. The sprint speed was higher for hatchlings from temperatures of 24 and 33°C. The growth rate of hatchlings was highest at 30°C; however, the survival rate of hatchlings was not affected by the thermal environment. This study demonstrated that even for a low-latitude margin population of the high-latitude lizard, Lacerta agilis, moderate warming (i.e., 27 and 30°C) would benefit embryonic and hatchling development. This was indicated by the results showing higher hatching success, growth rate, and survival rate. However, if temperatures increase above 33°C, development and survival would be depressed significantly. Thus, low-latitude margin population of high-latitude species Lacerta agilis would benefit from climate warming in the near future but would be under stress if the nest temperature exceeded 30°C.

Peroxisome proliferator-activated receptor gamma is essential for stress adaptation by maintaining lipid homeostasis in female fish

Reduction of lipid synthesis often causes free fatty acid (FFA) overload, resulting consequential oxidative stress and health damage. Environmental stresses also induce cellular oxidative stress in organisms. The functional peroxisome proliferator-activated receptor gamma (pparg) gene is essential for lipid synthesis and homeostatic lipid maintenance. However, the relationship between the pparg-mediated lipid synthesis and environmental stress adaptation awaits full elucidation. Here, we generated a pparg-knockout zebrafish model. The conversion of free fatty acids into triglycerides in the female pparg mutants was hampered by reduced esterification efficiency, thus induced lipotoxicity, as evidenced by high oxidative stress and damaged health in these mutants, which led to reduced resistance to cold, heat and ammonia nitrogen stresses. Activating pparg in the wild-type female fish via dietary supplementation with rosiglitazone (a pparg agonist), or reducing oxidative stress in the female pparg mutants via dietary supplementation with N-acetylcysteine (an antioxidant), or promoting mitochondrial fatty acid β-oxidation in the female pparg mutants via dietary supplementation with l-carnitine, resulted in significantly reduced cellular injury, and improved environmental stress resistance. Collectively, our findings reveal that the regulative function of pparg in FFA esterification is important in stress resistance in female fish, and highlight the tight correlation existing between lipotoxicity and environmental adaptation.

Starvation causes changes in the intestinal transcriptome and microbiome that are reversed upon refeeding

BACKGROUND

The ability of animals and their microbiomes to adapt to starvation and then restore homeostasis after refeeding is fundamental to their continued survival and symbiosis. The intestine is the primary site of nutrient absorption and microbiome interaction, however our understanding of intestinal adaptations to starvation and refeeding remains limited. Here we used RNA sequencing and 16S rRNA gene sequencing to uncover changes in the intestinal transcriptome and microbiome of zebrafish subjected to long-term starvation and refeeding compared to continuously fed controls.

RESULTS

Starvation over 21 days led to increased diversity and altered composition in the intestinal microbiome compared to fed controls, including relative increases in Vibrio and reductions in Plesiomonas bacteria. Starvation also led to significant alterations in host gene expression in the intestine, with distinct pathways affected at early and late stages of starvation. This included increases in the expression of ribosome biogenesis genes early in starvation, followed by decreased expression of genes involved in antiviral immunity and lipid transport at later stages. These effects of starvation on the host transcriptome and microbiome were almost completely restored within 3 days after refeeding. Comparison with published datasets identified host genes responsive to starvation as well as high-fat feeding or microbiome colonization, and predicted host transcription factors that may be involved in starvation response.

CONCLUSIONS

Long-term starvation induces progressive changes in microbiome composition and host gene expression in the zebrafish intestine, and these changes are rapidly reversed after refeeding. Our identification of bacterial taxa, host genes and host pathways involved in this response provides a framework for future investigation of the physiological and ecological mechanisms underlying intestinal adaptations to food restriction.

Temperature and Diet Acclimation Modify the Acute Thermal Performance of the Largest Extant Amphibian

The Chinese giant salamander (Andrias davidianus), one of the largest extant amphibian species, has dramatically declined in the wild. As an ectotherm, it may be further threatened by climate change. Therefore, understanding the thermal physiology of this species should be the priority to formulate related conservation strategies. In this study, the plasticity in metabolic rate and thermal tolerance limits of A. davidianus larvae were studied. Specifically, the larvae were acclimated to three temperature levels (7 °C, cold stress; 15 °C, optimum; and 25 °C, heat stress) and two diet items (red worm or fish fray) for 20 days. Our results indicated that cold-acclimated larvae showed increased metabolic capacity, while warm-acclimated larvae showed a decrease in metabolic capacity. These results suggested the existence of thermal compensation. Moreover, the thermal tolerance windows of cold-acclimated and warm-acclimated larvae shifted to cooler and hotter ranges, respectively. Metabolic capacity is not affected by diet but fish-fed larvae showed superiority in both cold and heat tolerance, potentially due to the input of greater nutrient loads. Overall, our results suggested a plastic thermal tolerance of A. davidianus in response to temperature and diet variations. These results are meaningful in guiding the conservation of this species.

The Influence of Hypothermia Hibernation Combined with CO2 Anesthesia on Life and Storage Quality of Large Yellow Croaker (Pseudosciaena crocea)

We explore the feasibility of the long-term transportation of live large yellow croakers (Pseudosciaena crocea) using the combined method of CO₂ anesthesia and hypothermia hibernation, and its effect on the quality of recovered fish stored at 4 °C. Fish treated with CO₂ anesthesia at a 2 ppm/s aeration rate were cooled at 3 °C/h to hibernate survived for 36 h at 8 °C in seawater. This method resulted in better survival rates and time, and a lower operational time than hypothermia hibernation or CO₂ anesthesia methods. The results of a blood analysis indicated that the stress experienced by the fish during hibernation was mitigated, but existent after recovery. The drip loss rate of the ordinary muscle of hibernated fish was significantly different from that of the control group at 4 °C, but there was no significant difference in the pH, lactic acid content, and color during early storage. Furthermore, hibernation did not affect springiness and chewiness. Thus, the combination of CO₂ anesthesia and hibernation may improve the survival and operation efficiency of fish in long-term transportation. However, this method affects the quality of fish after long-term storage. Thus, hibernated fish should be consumed after appropriate domestication or immediately after recovery.

C24:0 avoids cold exposure-induced oxidative stress and fatty acid β-oxidation damage

Low temperatures can cause severe growth inhibition and mortality in fish. Previous studies about the cold resistance of fish mainly focused on the role of unsaturated fatty acids, rather than saturated fatty acids (SFAs). In this study, the role of very-long-chain SFA synthetized by fatty acyl elongase 1 gene (elovl1) in cold resistance was explored. Both an aggravated liver oxidative stress and a mitochondrial metabolism disorder were observed in elovl1a^–/– and elovl1b^–/– zebrafish with cold stress. In vitro studies confirmed that high levels of C20:0 and C22:0 obviously increased the hepatocyte oxidative stress and activated the extracellular signal-regulated kinases 1/2 (Erk1/2) pathway to further induce apoptosis and inflammation. We further demonstrated that C24:0 could promote mitochondrial β-oxidation to improve the cold resistance of zebrafish. Overall, our results define a positive role of C24:0 fatty acids synthetized by elovl1 in the cold resistance of fish.

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elovl1, closely associated with C24:0, was activated in ZFL cells with cold stress

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C20:0 and C22:0 induced Erk1/2 expression and apoptosis to impair cold tolerance

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This study showed the positive role of C24:0 in the cold resistance of fish

Post-translational protein deimination signatures in sea lamprey (Petromyzon marinus) plasma and plasma-extracellular vesicles

Lampreys are a jawless vertebrate species belonging to an ancient vertebrate lineage that diverged from a common ancestor with humans ~500 million years ago. The sea lamprey (Petromyzon marinus) has a filter feeding ammocoete larval stage that metamorphoses into a parasitic adult, feeding both on teleost and elasmobranch fish. Lampreys are a valuable comparative model species for vertebrate immunity and physiology due to their unique phylogenetic position, unusual adaptive immune system, and physiological adaptions such as tolerance to salinity changes and urea. Peptidylarginine deiminases (PADs) are a phylogenetically conserved enzyme family which catalyses post-translational deimination/citrullination in target proteins, enabling proteins to gain new functions (moonlighting). The identification of deiminated protein targets in species across phylogeny may provide novel insights into post-translational regulation of physiological and pathophysiological processes. Extracellular vesicles (EVs) are membrane vesicles released from cells that carry cargos of small molecules and proteins for cellular communication, involved in both normal and pathological processes. The current study identified deimination signatures in proteins of both total plasma and plasma-EVs in sea lamprey and furthermore reports the first characterisation of plasma-EVs in lamprey. EVs were poly-dispersed in the size range of 40-500 nm, similar to what is observed in other taxa, positive for CD63 and Flotillin-1. Plasma-EV morphology was confirmed by transmission electron microscopy. Assessment of deimination/citrullination signatures in lamprey plasma and plasma-EVs, revealed 72 deimination target proteins involved in immunity, metabolism and gene regulation in whole plasma, and 37 target proteins in EVs, whereof 24 were shared targets. Furthermore, the presence of deiminated histone H3, indicative of gene-regulatory mechanisms and also a marker of neutrophil extracellular trap formation (NETosis), was confirmed in lamprey plasma. Functional protein network analysis revealed some differences in KEGG and GO pathways of deiminated proteins in whole plasma compared with plasma-EVs. For example, while common STRING network clusters in plasma and plasma-EVs included Peptide chain elongation, Viral mRNA translation, Glycolysis and gluconeogenesis, STRING network clusters specific for EVs only included: Cellular response to heat stress, Muscle protein and striated muscle thin filament, Nucleosome, Protein processing in endoplasmic reticulum, Nucleosome and histone deacetylase complex. STRING network clusters specific for plasma were: Adipokinetic hormone receptor activity, Fibrinogen alpha/beta chain family, peptidase S1A, Glutathione synthesis and recycling-arginine, Fructose 1,6-bisphosphate metabolic process, Carbon metabolism and lactate dehydrogenase activity, Post-translational protein phosphorylation, Regulation of insulin-like growth factor transport and clotting cascade. Overall, for the EV citrullinome, five STRING network clusters, 10 KEGG pathways, 15 molecular GO pathways and 29 Reactome pathways were identified, compared with nine STRING network clusters, six KEGG pathways, two Molecular GO pathways and one Reactome pathway specific for whole plasma; while further pathways were shared. The reported findings indicate that major pathways relevant for immunity and metabolism are targets of deimination in lamprey plasma and plasma-EVs, with some differences, and may help elucidating roles for the conserved PAD enzyme family in regulation of immune and metabolic function throughout phylogeny.

Transcriptional response to cold and fasting acclimation in Onychostoma macrolepis during the overwintering stage

In this study, we investigated the transcriptome responses of the liver of Onychostoma macrolepis in by RNA sequencing. The sampling process involved three groups: 1G (0 week, 10 °C), 2G (12 weeks, 0 °C) and 3G (24 weeks, 10 °C). The body weight, viscera index, hepatopancreas index and intraperitoneal fat index of O. macrolepis showed a decreasing trend with the prolonging of overwintering time. The crude fat contents of whole fish, muscle and liver in O. macrolepis after overwintering were significantly lower than those of the fish before overwintering (p < 0.05). In 1G versus 2G group, 2G versus 3G group and 1G versus 3G group, the differently expressed genes (DEGs) were 4630, 3976 and 2311, respectively. These results indicated that different stages of overwintering period had significant effects on gene expression of O. macrolepis, and the influence degree gradually decreased with the extension of overwintering period. The results of Gene ontology (GO) enrichment showed that these DEGs were mainly related to metabolism and immunity, and most of them were down-regulated. In this study, the KEGG pathway classification results showed that signal transduction was the most representative. In addition, KOG enrichment results showed that many DEGs associated with lipid transport and metabolism were down-regulated during the overwintering period. These observations suggested that slowing metabolism and delaying immunity may be the strategies for overwintering adaptation of O. macrolepis.

Alteration and the Function of Intestinal Microbiota in High-Fat-Diet- or Genetics-Induced Lipid Accumulation

Diet and host genetics influence the composition of intestinal microbiota, yet few studies have compared the function of intestinal microbiota in the diet- or genotype-induced lipid deposition, which limits our understanding of the role of intestinal bacteria in metabolic disorders. The lipid accumulation in wild-type zebrafish fed with control (CON) or high-fat (HF) diet and two gene-knockout zebrafish lines (cpt1b^–/– or pparab^–/–) fed with control diet was measured after a 4-week feeding experiment. The intestinal microbiota composition of these groups was investigated using 16S ribosomal RNA (rRNA) gene sequencing (DNA-based) and 16S rRNA sequencing (RNA-based). The HF diet or deficiency of two genes induced more weight gain and higher triglyceride content in the liver compared with their control group. 16S rRNA gene sequencing (DNA-based) indicated the decreased abundance of Proteobacteria in the HF group compared with CON, but there was no significant difference in bacterial α diversity among treatments. 16S rRNA sequencing (RNA-based) confirmed the decreased abundance of Proteobacteria and the bacterial α diversity in the HF group compared with CON. Deficiency of cpt1b or pparab showed less change in microbiota composition compared with their wild-type group. Intestinal microbiota of each group was transferred to germ-free zebrafish, and the quantification of Nile red staining indicated that the intestinal microbiota of the HF group induced more lipid accumulation compared with CON, whereas intestinal microbiota of cpt1b^–/– and pparab^–/– zebrafish did not. The results showed that RNA-based bacterial sequencing revealed more bacterial alteration than DNA-based bacterial sequencing. HF diet had a more dominant role in shaping gut microbiota composition to induce lipid accumulation compared with the gene-knockout of cpt1b or pparab in zebrafish, and the transplant of intestinal microbiota from HF-fed fish induced more lipid deposition in germ-free zebrafish. Together, these data suggested that a high-fat diet exerted a more dominant role over the deletion of cpt1b or pparab on the intestinal bacterial composition, which corresponded to lipid accumulation.

Harnessing the potential of cross-protection stressor interactions for conservation: a review

Conservation becomes increasingly complex as climate change exacerbates the multitude of stressors that organisms face. To meet this challenge, multiple stressor research is rapidly expanding, and the majority of this work has highlighted the deleterious effects of stressor interactions. However, there is a growing body of research documenting cross-protection between stressors, whereby exposure to a priming stressor heightens resilience to a second stressor of a different nature. Understanding cross-protection interactions is key to avoiding unrealistic 'blanket' conservation approaches, which aim to eliminate all forms of stress. But, a lack of synthesis of cross-protection interactions presents a barrier to integrating these protective benefits into conservation actions. To remedy this, we performed a review of cross-protection interactions among biotic and abiotic stressors within a conservation framework. A total of 66 publications were identified, spanning a diverse array of stressor combinations and taxonomic groups. We found that cross-protection occurs in response to naturally co-occurring stressors, as well as novel, anthropogenic stressors, suggesting that cross-protection may act as a 'pre-adaptation' to a changing world. Cross-protection interactions occurred in response to both biotic and abiotic stressors, but abiotic stressors have received far more investigation. Similarly, cross-protection interactions were present in a diverse array of taxa, but several taxonomic groups (e.g. mammals, birds and amphibians) were underrepresented. We conclude by providing an overview of how cross-protection interactions can be integrated into conservation and management actions and discuss how future research in this field may be directed to improve our understanding of how cross-protection may shield animals from global change.

Lipolysis and lipophagy play individual and interactive roles in regulating triacylglycerol and cholesterol homeostasis and mitochondrial form in zebrafish

Neutral lipases-mediated lipolysis and acid lipases-moderated lipophagy are two main processes for degradation of lipid droplets (LDs). However, the individual and interactive roles of these metabolic pathways are not well known across vertebrates. This study explored the roles of lipolysis and lipophagy from the aspect of neutral and acid lipases in zebrafish. We established zebrafish strains deficient in either adipose triglyceride lipase (atgl^-/-; AKO fish) or lysosomal acid lipase (lal^-/-; LKO fish) respectively, and then inhibited lipolysis in the LKO fish and lipophagy in the AKO fish by feeding diets supplemented with the corresponding inhibitors Atglistatin and 3-Methyladenine, respectively. Both the AKO and LKO fish showed reduced growth, swimming activity, and oxygen consumption. The AKO fish did not show phenotypes in adipose tissue, but mainly accumulated triacylglycerol (TAG) in liver, also, they had large LDs in the hepatocytes, and did not stimulate lipophagy as a compensation response but maintained basal lipophagy. The LKO fish reduced total lipid accumulation in the body but had high cholesterol content in liver; also, they accumulated small LDs in the hepatocytes, and showed increased lipolysis, especially Atgl expression, as a compensatory mechanism. Simultaneous inhibition of lipolysis and lipophagy in zebrafish resulted in severe liver damage, with the potential to trigger mitophagy. Overall, our study illustrates that lipolysis and lipophagy perform individual and interactive roles in maintaining homeostasis of TAG and cholesterol metabolism. Furthermore, the interactive roles of lipolysis and lipophagy may be essential in regulating the functions and form of mitochondria.

Metabolomics analysis of the effects of temperature on the growth and development of juvenile European seabass (Dicentrarchus labrax)

Temperature variations have significant impacts on the growth and development of fish. In this study, the effects of temperature on the growth and development of European seabass (Dicentrarchus labrax) were investigated using ultra-performance liquid chromatography-tandem mass spectrometry-based metabolomics. Three groups of fish were exposed to various temperatures for 60 days: T1-E (10 °C), T2-E (15 °C), and T3-E (20 °C). Afterward, the temperature of all groups was increased to 20 °C and maintained for 62 days (T1-S, T2-S, T3-S). The livers were extracted for subsequent analysis. In the first stage of the experiment, the growth rate was highest in the T3-E group, followed by the T1-E and T2-E groups. The following metabolites identified by comparative analysis were found to be elevated: L-thyroxine, cysteamine, uridine diphosphate (UDP)-glucose, α-ketoglutaric acid, carbamoyl phosphate, and guanidine acetic acid of the T1-E group. Pathway analysis of the altered metabolites suggested changes in glucose metabolism, arginine and proline metabolism, the tricarboxylic acid cycle, the ornithine cycle, histidine metabolism, and taurine metabolism, which were involved with growth and development. Meanwhile, partial compensatory growth was observed in fish in the T1-S and T2-S groups. Metabolites identified as potential markers of growth included L-cysteine, taurocholic acid, UDP-glucose, and L-thyroxine. The significantly changed metabolic pathways were cysteine and methionine metabolism, bile secretion, tyrosine metabolism, and hypotaurine metabolism. We screened out the marker metabolites and metabolic pathway could provide important insights into the potential mechanisms of temperature affects the growth and development of European seabass. All in all, our research can provide theoretical basis and technical guidance for efficiently culturing European seabass.

Myo-inositol improves growth performance and regulates lipid metabolism of juvenile Chinese mitten crab (Eriocheir sinensis) fed different percentage of lipid

This study evaluated the effects of dietary myo-inositol (MI) on growth performance, antioxidant status and lipid metabolism of juvenile Chinese mitten crab (Eriocheir sinensis) fed different percentage of lipid. Crabs (4·58 (sem 0·05) g) were fed four diets including a normal lipid diet (N, containing 7 % lipid and 0 mg/kg MI), N with MI supplementation (N + MI, containing 7 % lipid and 1600 mg/kg MI), a high lipid diet (H, containing 13 % lipid and 0 mg/kg MI) and H with MI supplementation (H + MI, containing 13 % lipid and 1600 mg/kg MI) for 8 weeks. The H + MI group showed higher weight gain and specific growth rate than those in the H group. The dietary MI could improve the lipid accumulations in the whole body, hepatopancreas and muscle as a result of feeding on the high dietary lipid (13 %) in crabs. Besides, the crabs fed the H + MI diets increased the activities of antioxidant enzymes but reduced the malondialdehyde content in hepatopancreas compared with those fed the H diets. Moreover, dietary MI enhanced the expression of genes involved in lipid oxidation and exportation, yet reduced lipid absorption and synthesis genes expression in the hepatopancreas of crabs fed the H diet, which might be related to the activation of inositol 1,4,5-trisphosphate receptor (IP3R)/calmodulin-dependent protein kinase kinase-β (CaMKKβ)/adenosine 5'-monophosphate-activated protein kinase (AMPK) signalling pathway. This study demonstrates that MI could increase lipid utilisation and reduce lipid deposition in the hepatopancreas of E. sinensis fed a high lipid diet through IP3R/CaMKKβ/AMPK activation. This work provides new insights into the function of MI in the diet of crustaceans.

Fasting ameliorates oxidative stress: A review of physiological strategies across life history events in wild vertebrates

Fasting is a component of many species' life history due to environmental factors or behavioral patterns that limit access to food. Despite metabolic and physiological challenges associated with these life history stages, fasting-adapted wild vertebrates exhibit few if any signs of oxidative stress, suggesting that fasting promotes redox homeostasis. Here we review mammalian, avian, reptilian, amphibian, and piscine examples of animals undergoing fasting during prolonged metabolic suppression (e.g. hibernation and estivation) or energetically demanding processes (e.g. migration and breeding) to better understand the mechanisms underlying fasting tolerance in wild vertebrates. These studies largely show beneficial effects of fasting on redox balance via limited oxidative damage. Though some species exhibit signs of oxidative stress due to energetically or metabolically extreme processes, fasting wild vertebrates largely buffer themselves from the negative consequences of oxidative damage through specific strategies such as elevating antioxidants, selectively maintaining redox balance in critical tissues, or modifying behavioral patterns. We conclude with suggestions for future research to better elucidate the protective effects of fasting on oxidative stress as well as disentangle the impacts from other life history stages. Further research in these areas will facilitate our understanding of the mechanisms wild vertebrates use to mitigate the negative impacts associated with metabolically-extreme life history stages as well as potential translation into therapeutic interventions in non-fasting-adapted species including humans.

Inhibition of Embryonic HSP 90 Function Promotes Variation of Cold Tolerance in Zebrafish

Accumulating evidence indicates that heat shock protein 90 (HSP90) plays essential roles in modulation of phenotypic plasticity in vertebrate development, however, the roles of HSP90 in modulation of cold tolerance capacity in fish are still unclear. In the present study, we showed that transient inhibition of embryonic HSP90 function by a chemical inhibitor or low conductivity stress promoted variation of cold tolerance capacity in adult zebrafish. Further work showed that embryonic HSP90 inhibition enhanced cold tolerance in adult zebrafish could be transmitted to their offspring. RNA-seq data showed that embryonic HSP90 inhibition enhanced cold tolerance involves variation of gene expression related to proteasome, lysosome, autophagy, and ribosome. Experiments with zebrafish ZF4 cells showed that two differentially expressed genes atg9b and psmd12 were up-regulated by radicicol treatment and provided protective roles for cells under cold stress, indicating that up-regulation of autophagy and proteasome function contributes to enhanced cold tolerance. The present work sheds a light on the roles of HSP90 in regulation of phenotypic plasticity associated with thermal adaptation in fish.

Distinct dietary cadmium toxic effects and defense strategies in two strains of gibel carp (Carassius gibelio) revealed by a comprehensive perspective

Previous studies demonstrated that gibel carp A strain was more susceptible to herpesvirus infection than other strains. Thus, we hypothesized that F strain might display better defense responses than the A strain against cadmium (Cd) exposure. To test our hypothesis, gibel carp A strain and F strain were exposed to three diets comprising of different concentrations of Cd for 8 weeks to compare their resistances to Cd. Comprehensive evaluations on biochemical, physiological and histological responses were conducted post-exposure. Results showed that no adverse effects and differences were observed on growth in two strains of gibel carp, compromising of the remarkable hepatoxicity-caused liver damage as shown by histological observations. Dietary Cd exposure stimulated antioxidant defense in the liver to counteract the Cd hepatoxicity, especially in the F strain. Activation of ER stress response positively stimulated the autophagy, then triggering apoptosis in fish after dietary Cd exposure. Thus, Cd-induced autophagy served as a protective strategy to alleviate hepatoxicity, but overaction of ER stress also triggered irreparable cell death via apoptosis. Cd induced dysregulation of lipid accumulation, which might be a common mechanism in response to hepatoxicity. Last but not least, the F strain showed stronger response on antioxidant, ER stress and autophagy, but apoptosis were remitted compared with the A strain, implying the F strain showed stronger response but better defense strategies to dietary Cd exposure. Our finding provides useful information for genetic breeding in aquaculture, and ultimately contribute to the safety assessment of aquatic products for human consumption.

The health and condition responses of Delta Smelt to fasting: A time series experiment

There is an extensive literature establishing, validating, and quantifying a wide range of responses of fishes to fasting. Our study complements this work by comparing fed and unfed treatments of hatchery-raised Delta Smelt (Hypomesus transpacificus)-an imperiled fish that is endemic to the San Francisco Estuary and its tributaries in California, USA-across a diverse suite of endpoints over a two-month time series. The experiment was conducted at 15.9°C, and individuals were sampled at 12 time points as starvation became increasingly severe. We found that hepatosomatic index and condition factor were relatively sensitive to starvation, becoming significantly depressed at Day 4 and 7, respectively. Histological analysis of liver showed elevated cytoplasmic inclusion bodies at Day 7, followed by increased glycogen depletion, single cell necrosis, and hydropic vacuolar degeneration at Day 14, 21, and 28, respectively. Of four antioxidants measured, glutathione decreased at Day 4, superoxide dismutase increased at Day 14, catalase increased at Day 56, and glutathione peroxidase was not affected by starvation. The net result was a ~2-fold increase in lipid peroxidation (malondialdehyde) in fasted fish that was highly inconsistent through time. RNA to DNA ratio and triglycerides in muscle were relatively insensitive to starvation, only consistently decreasing with fasting after mortality began increasing in the 'No Feeding' treatment, at Day 21. Together, these results suggest that Delta Smelt mobilize hepatic energy stores far more rapidly than lipids in muscle when subjected to fasting, leading to rapid atrophy of liver and the development of cytoplasmic inclusion bodies-possibly autophagosomes-in hepatocytes.

Gemfibrozil improves lipid metabolism in Nile tilapia Oreochromis niloticus fed a high-carbohydrate diet through peroxisome proliferator activated receptor-α activation

High carbohydrate diet (HCD) can induce lipid metabolism disorder, characterized by excessive lipid in farmed fish. Peroxisome proliferator activated receptor-α (PPARα) plays an important role in lipid homeostasis. In this study, we hypothesize that PPARα can improve lipid metabolism in fish fed HCD. Fish (3.03 ± 0.11 g) were fed with three diets: control (30% carbohydrate), HCD (45% carbohydrate) and HCG (HCD supplemented with 200 mg/kg gemfibrozil, an agonist of PPARα) for eight weeks. The fish fed HCG had higher growth rate and protein effiency than those fed the HCD diet, whereas the opposite trend was observed in feed conversion ratio, hepatosomatic index and mesenteric fat index. Additionally, fish fed HCG significantly decreased lipid accumulation in the whole body, liver and adipose tissues compared to those fed the HCD diet. Furthermore, fish in the HCG group significantly increased the mRNA and protein expression and protein dephosphorylation of PPARα. The HCG group also significantly increased the mRNA level of the downstream target genes of PPARα, whereas the opposite trend occured in the mRNA level of lipolysis-related genes compared to the HCD group. Besides, fish in the HCG group remarkably decreased the contents of alanine aminotransferase, aspartate aminotransferase and malondialdehyde, whereas the opposite occured in the activities of antioxidative enzymes and anti-inflammatory cytokine genes compared to the HCD group. This study indicates that gemfibrozil can improve lipid metabolism and maintain high antioxidant and anti-inflammatory capacity through activating PPARα in Nile tilapia fed a high carbohydrate diet.

Zebrafish as a model to study autophagy and its role in skeletal development and disease

In the last twenty years, research using zebrafish as a model organism has increased immensely. With the many advantages that zebrafish offer such as high fecundity, optical transparency, ex vivo development, and genetic tractability, they are well suited to studying developmental processes and the effect of genetic mutations. More recently, zebrafish models have been used to study autophagy. This important protein degradation pathway is needed for cell and tissue homeostasis in a variety of contexts. Correspondingly, its dysregulation has been implicated in multiple diseases including skeletal disorders. In this review, we explore how zebrafish are being used to study autophagy in the context of skeletal development and disease, and the ways these areas are intersecting to help identify potential therapeutic targets for skeletal disorders.