Dietary methionine level affects growth performance and hepatic gene expression of GH-IGF system and protein turnover regulators in rainbow trout (Oncorhynchus mykiss) fed plant protein-based diets

Effects of essential amino acids supplementation in a low-protein diet on growth performance, intestinal health and microbiota of juvenile blotched snakehead (Channa maculata)

Developing a low-protein feed is important for the sustainable advancement of aquaculture. The aim of this study was to investigate the effects of essential amino acid (EAA) supplementation in a low-protein diet on the growth, intestinal health, and microbiota of the juvenile blotched snakehead, Channa maculata in an 8-week trial conducted in a recirculating aquaculture system. Three isoenergetic diets were formulated to include a control group (48.66 % crude protein (CP), HP), a low protein group (42.54 % CP, LP), and a low protein supplementation EAA group (44.44 % CP, LP-AA). The results showed that significantly lower weight gain (WG), specific growth rate (SGR), protein efficiency ratio (PER), and feed efficiency ratio (FER) were observed in fish that were fed LP than in the HP and LP-AA groups (P < 0.05). The HP and LP-AA groups exhibited a significant increase in intestinal villus length, villus width, and muscular thickness compared to the LP group (P < 0.05). Additionally, the HP and LP-AA groups demonstrated significantly higher levels of intestinal total antioxidant capacity (T-AOC), catalase (CAT), and superoxide dismutase (SOD) and lower levels of malondialdehyde (MDA) compared to the LP group (P < 0.05). The apoptosis rate of intestinal cells in the LP group was significantly higher than those in the LP and HP groups (P < 0.05). The mRNA expression levels of superoxide dismutase (sod), nuclear factor kappa B p65 subunit (nfκb-p65), heat shock protein 70 (hsp70), and inhibitor of NF-κBα (iκba) in the intestine were significantly higher in the LP group than those in the HP and LP-AA groups (P < 0.05). The 16s RNA analysis indicated that EAA supplementation significantly increased the growth of Desulfovibrio and altered the intestinal microflora. The relative abundances of Firmicutes and Cyanobacteria were positively correlated with antioxidant parameters (CAT and T-AOC), whereas Desulfobacterota was negatively correlated with sod and T-AOC. The genera Bacillus, Bacteroides, and Rothia were associated with the favorable maintenance of gut health. In conclusion, dietary supplementation with EAAs to achieve a balanced amino acid profile could potentially reduce the dietary protein levels from 48.66 % to 44.44 % without adversely affecting the growth and intestinal health of juvenile blotched snakeheads.

Effects of supplementing coated methionine in a high plant-protein diet on growth, antioxidant capacity, digestive enzymes activity and expression of TOR signaling pathway associated genes in gibel carp, Carassius auratus gibelio

This study explored the impacts of supplementation of different levels of coated methionine (Met) in a high-plant protein diet on growth, blood biochemistry, antioxidant capacity, digestive enzymes activity and expression of genes related to TOR signaling pathway in gibel carp (Carassius auratus gibeilo). A high-plant protein diet was formulated and used as a basal diet and supplemented with five different levels of coated Met at 0.15, 0.30, 0.45, 0.60 and 0.75%, corresponding to final analyzed Met levels of 0.34, 0.49, 0.64, 0.76, 0.92 and 1.06%. Three replicate groups of fish (initial mean weight, 11.37 ± 0.02 g) (20 fish per replicate) were fed the test diets over a 10-week feeding period. The results indicated that with the increase of coated Met level, the final weight, weight gain (WG) and specific growth rate initially boosted and then suppressed, peaking at 0.76% Met level (P< 0.05). Increasing dietary Met level led to significantly increased muscle crude protein content (P< 0.05) and reduced serum alanine aminotransferase activity (P< 0.05). Using appropriate dietary Met level led to reduced malondialdehyde concentration in hepatopancreas (P< 0.05), improved superoxide dismutase activity (P< 0.05), and enhanced intestinal amylase and protease activities (P< 0.05). The expression levels of genes associated with muscle protein synthesis such as insulin-like growth factor-1, protein kinase B, target of rapamycin and eukaryotic initiation factor 4E binding protein-1 mRNA were significantly regulated, peaking at Met level of 0.76% (P< 0.05). In conclusion, supplementing optimal level of coated Met improved on fish growth, antioxidant capacity, and the expression of TOR pathway related genes in muscle. The optimal dietary Met level was determined to be 0.71% of the diet based on quadratic regression analysis of WG.

Exploring the physiological plasticity of giant grouper (Epinephelus lanceolatus) to dietary sulfur amino acids and taurine to measure dietary requirements and essentiality

Giant grouper (Epinephelus lanceolatus) is an economically important yet under-researched species, still reliant on 'trash fish' or generic aquafeeds. The transition toward sustainable formulations is contingent on establishing requirements of target species for limiting nutrients, among which the sulfur amino acids (methionine and cysteine) commonly limit fish growth. Further, there remains significant conjecture around the role of the sulfonic acid taurine in marine aquafeed formulation and its relationship to sulfur amino acids. To develop a species-specific feed formulation for giant grouper, dietary methionine was modulated in a dose-response experiment to achieve five graded levels from 9.5 to 21.5 g/kg, including an additional diet with methionine at 18.6 g/kg supplemented with 8 g/kg taurine. The mean (±SD) cysteine level of the diets was 4.5 ± 0.3 g/kg. Each diet was randomly allocated to triplicate tanks of 14 fish (83.9 ± 8.4 g). The best-fit regression for growth showed that the optimal dietary methionine content was 15.8 g/kg and the total sulfur amino acid content was 20.3 g/kg. Inadequate dietary methionine content triggered physiological responses, including hepatic hyperplasia and hypoplasia at 9.5 and 21.5 g/kg, respectively, and high aspartate transaminase levels at 18.9 g/kg. Moreover, inadequate dietary methionine contents resulted in higher densities of mixed goblet cell mucin and reduced absorptive surface area of posterior intestinal villi. Our results suggest that adequate levels of methionine, but not taurine, improved posterior intestinal conditions and liver homeostasis. These findings may aid in formulating aquafeeds to optimize gastrointestinal and liver functions in juvenile giant grouper.

Insulin-like growth factor-1 (Igf1) signaling responses to food consumption after fasting in the Pacific rockfish Sebastes carnatus

Fish adjust rates of somatic growth in the face of changing food consumption. As in other vertebrates, growth in fish is regulated by the growth hormone (Gh)/insulin-like growth factor-1 (Igf1) endocrine axis, and changes in food intake impact growth via alterations to Gh/Igf1 signaling. Understanding the time course by which the Gh/Igf1 axis responds to food consumption is crucial to predict how rapidly changes in food abundance might lead to altered growth dynamics. Here, we looked at the response times of plasma Igf1 and liver Igf1 signaling-associated gene expression to refeeding after food deprivation in juvenile gopher rockfish (Sebastes carnatus), one of several species of northern Pacific Ocean Sebastes rockfishes targeted by fisheries or utilized for aquaculture. Gopher rockfish were fasted for 30 d, after which a subset was fed to satiation for 2 h, while other rockfish continued to be fasted. Refed fish exhibited higher hepatosomatic index (HSI) values and increased Igf1 after food consumption. Gene transcripts for Gh receptor 1 (ghr1), but not ghr2, increased in the liver after eating. Transcripts encoding igf1 also increased in the liver of refed fish 2-4 d after feeding, only to return to levels similar as continually fasted rockfish by 9 d after feeding. Liver mRNA abundances for Igf binding protein (Igfbp) genes igfbp1a, igfbp1b, and igfbp3a declined within 2 d of feeding. These findings provide evidence that circulating Igf1 in rockfish reflects a fish's feeding experience within the previous few days, and suggest that feeding-induced increases in Igf1 are being mediated in part by altered liver sensitivity to Gh due to upregulated Gh receptor 1 expression.

Spirulina-enriched Substrate to Rear Black Soldier Fly (Hermetia illucens) Prepupae as Alternative Aquafeed Ingredient for Rainbow Trout (Oncorhynchus mykiss) Diets: Possible Effects on Zootechnical Performances, Gut and Liver Health Status, and Fillet Quality

In the present study, an organic substrate (coffee silverskin) enriched with spirulina (Arthrospira platensis; 15% w/w), as a source of lipids and bioactive molecules, was used to rear the black soldier fly (Hermetia illucens) prepupae. Three grossly isonitrogenous, isoproteic, isolipidic and isoenergetic experimental diets for rainbow trout (Oncorhynchus mykiss) juveniles were then produced: a control diet (HM0) mostly including fish meal and fish oil, and two other test diets named HM3 and HM20, in which 3 or 20% of the marine ingredients were substituted with full fat black soldier fly prepupae meal (HM), respectively. Experimental diets were provided for 6 weeks, and at the end of the trial the physiological responses and marketable traits of the fish were investigated using a multidisciplinary approach. Generally, all test diets were well accepted, and fish growth, gut and liver health status, and marketable characteristics were not impaired by the experimental diets. However, an increased immuno-related gene expression along with a slight reduction of fillet redness and yellowness was evident in fish from the HM20 group.

Metabolic and molecular signatures of improved growth in Atlantic salmon (Salmo salar) fed surplus levels of methionine, folic acid, vitamin B6 and B12 throughout smoltification

A moderate surplus of the one carbon (1C) nutrients methionine, folic acid, vitamin B₆ and B₁₂ above dietary recommendations for Atlantic salmon has shown to improve growth and reduce hepatosomatic index in the on-growing saltwater period when fed throughout smoltification. Metabolic properties and molecular mechanisms determining the improved growth are unexplored. Here, we investigate metabolic and transcriptional signatures in skeletal muscle taken before and after smoltification to acquire deeper insight into pathways and possible nutrient–gene interactions. A control feed (Ctrl) or 1C nutrient surplus feed (1C+) were fed to Atlantic salmon 6 weeks prior to smoltification until 3 months after saltwater transfer. Both metabolic and gene expression signatures revealed significant 1C nutrient-dependent changes already at pre-smolt, but differences intensified when analysing post-smolt muscle. Transcriptional differences revealed lower expression of genes related to translation, growth and amino acid metabolisation in post-smolt muscle when fed additional 1C nutrients. The 1C+ group showed less free amino acid and putrescine levels, and higher methionine and glutathione amounts in muscle. For Ctrl muscle, the overall metabolic profile suggests a lower amino acid utilisation for protein synthesis, and increased methionine metabolisation in polyamine and redox homoeostasis, whereas transcription changes are indicative of compensatory growth regulation at local tissue level. These findings point to fine-tuned nutrient–gene interactions fundamental for improved growth capacity through better amino acid utilisation for protein accretion when salmon was fed additional 1C nutrients throughout smoltification. It also highlights potential nutritional programming strategies on improved post-smolt growth through 1C+ supplementation before and throughout smoltification.

Amino Acids and IGF1 Regulation of Fish Muscle Growth Revealed by Transcriptome and microRNAome Integrative Analyses of Pacu (Piaractus mesopotamicus) Myotubes

Amino acids (AA) and IGF1 have been demonstrated to play essential roles in protein synthesis and fish muscle growth. The myoblast cell culture is useful for studying muscle regulation, and omics data have contributed enormously to understanding its molecular biology. However, to our knowledge, no study has performed the large-scale sequencing of fish-cultured muscle cells stimulated with pro-growth signals. In this work, we obtained the transcriptome and microRNAome of pacu (Piaractus mesopotamicus)-cultured myotubes treated with AA or IGF1. We identified 1228 and 534 genes differentially expressed by AA and IGF1. An enrichment analysis showed that AA treatment induced chromosomal changes, mitosis, and muscle differentiation, while IGF1 modulated IGF/PI3K signaling, metabolic alteration, and matrix structure. In addition, potential molecular markers were similarly modulated by both treatments. Muscle-miRNAs (miR-1, -133, -206 and -499) were up-regulated, especially in AA samples, and we identified molecular networks with omics integration. Two pairs of genes and miRNAs demonstrated a high-level relationship, and involvement in myogenesis and muscle growth: marcksb and miR-29b in AA, and mmp14b and miR-338-5p in IGF1. Our work helps to elucidate fish muscle physiology and metabolism, highlights potential molecular markers, and creates a perspective for improvements in aquaculture and in in vitro meat production.

Concurrent changes in thermal tolerance thresholds and cellular heat stress response reveals novel molecular signatures and markers of high temperature acclimation in rainbow trout

The objective of this study was to better understand the molecular mechanisms which regulate acclimatory responses and thermal safety margins of rainbow trout (Oncorhynchus mykiss) at temperatures above physiological optimum. For this, we investigated the time course of changes in critical thermal tolerance thresholds and associated hepatic and renal transcript abundance of molecular markers related to cellular stress response, during high temperature acclimation. The experimental fish were initially acclimated to 17 °C and later exposed to a gradually raised elevated temperature regime (22 °C) for a period of 30 days. CT_max, CT_min and mRNA expression of candidate markers were examined before the thermal challenge (T₀) and over the time-course (days) of high temperature exposure (T₁, T₃, T₇, T₁₅ and T₃₀). With respect to organismal response, CT_max was significantly elevated at T₃, but the degree of gain in heat tolerance was not persistent. Contrarily, we observed a gradual loss in cold tolerance with highest CT_min estimate at T₃₀. Based on the time-course of mRNA expression, the studied markers could be categorized into those which were persistently elevated (hsp70a, hsp70b, hspa5, hsp90a, hsp90b, stip1 and serpinh1 in kidney and hsp90b in liver); those which concurred with changes in CT_min (hspbp1, hsp90b, stip1, gr1, hif1a, hyou1, tnfa and tlr5 in kidney); and those which concurred with changes in CT_max (hsp90a, serpinh1, tlr5 and lmo2 in liver). Apparently, transcriptional changes in kidney and liver reflected CT_min and CT_max trend, respectively. Expression profile of stip1 and tlr5 suggest that they are potential novel markers which could reflect thermal limits in rainbow trout. Hepatic metabolic markers were either initially elevated (alt, glud, g6pase1) or down-regulated at different time-points (ast2, gls1, fas, cpt1b, mtor), linked to gluconeogenesis and metabolic depression, respectively. Whereas, growth-axis markers showed no significant differences. Overall, this time-course analysis has revealed potential associations in organismal and tissue-specific cellular response to high temperature acclimation in a thermally sensitive coldwater ectotherm.

Dietary tryptophan supplementation does not affect growth but increases brain serotonin level and modulates the expression of some liver genes in zebrafish (Danio rerio)

This study aimed at assessing the effects of the dietary tryptophan (Trp) supplementation on growth and feed utilization, brain serotonin content, and expression of selected liver genes (involved in the liver serotonin pathway, protein synthesis degradation, and antioxidant activity) in zebrafish. A growth trial was conducted with zebrafish juveniles fed five experimental isoproteic (40%DM) and isolipidic (8%DM) fishmeal-based diets containing graded levels of Trp: a Trp-non-supplemented diet (diet Trp0, with 0.22% Trp) and four Trp-supplemented diets containing 2-16 times higher Trp content (diets Trp2, Trp4, Trp8, and Trp16 with 0.40, 0.91, 2.02, and 3.34% Trp, respectively). Diets were tested in quadruplicate, with fish being fed twice a day, 6 days a week for 6 weeks to apparent visual satiation. At the end of the trial, growth performance and feed utilization were assessed, and fish from all experimental groups were sampled for whole-body composition analysis. In addition, fish fed low (Trp0), medium (Trp4), and high (Trp16) Trp diets were also sampled for analysis of brain serotonin content and liver gene expression. Tested tryptophan levels did not influence growth performance nor feed intake. However, values of energy and nitrogen retention as well as body energy content indicate a better feed utilization with diets containing around 0.9% and 2.0% DM Trp. Brain serotonin content increased with increasing dietary tryptophan levels. In addition, regarding liver genes, dietary treatment had a modulatory effect on the expression of Htr1aa and Htr2cl1 genes (encoding for serotonin receptors), TPH1a gene (encoding for tryptophan hydroxylase, the rate-limiting enzyme in the synthesis of serotonin from tryptophan), TOR gene (involved in protein synthesis), and Keap1 gene (involved in antioxidant responses).

Excessive Dietary Lipid Affecting Growth Performance, Feed Utilization, Lipid Deposition, and Hepatopancreas Lipometabolism of Large-Sized Common Carp (Cyprinus carpio)

An 82-day study was conducted to assess the effect of the dietary lipid levels on growth performance, feed utilization, lipid deposition, and hepatopancreas lipometabolism of large-sized common carp (Cyprinus carpio). Six isonitrogenous (300 g/kg protein) pelletized diets with different dietary lipid levels (30, 60, 90, 120, 150, and 180 g/kg) were fed in triplicate to fish groups with 75 individuals (with an initial mean weight of 247.00 ± 16.67 g). The results showed that there was a significant increase in weight gain (WG) rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) as dietary lipid levels increased from 30 to 60 g/kg (p < 0.05) and then there was a decline. Feed conversion rate (FCR) was observed to be significantly lower in 60 g/kg lipid treatments (p < 0.05). Muscle crude protein contents were obtained to be significantly higher in 60 and 90 g/kg treatments (p < 0.05). The crude lipid content in the hepatopancreas increased significantly with an increase in dietary lipid levels (p < 0.05). The expression of lipoprotein lipase (LPL) and carnitine palmitoyltransferase-1 (CPT1) in the hepatopancreas was significantly downregulated with an increase in dietary lipid levels while the expression of growth hormone (GH), insulin-like growth factor-1 (IGF-1), fatty acid synthase (FAS), acetyl-CoA carboxylase-1 (ACC-1), and sterol regulatory element binding protein (SREBP) was upregulated first in 30 and 60 g/kg lipid treatments and then downregulated significantly in other treatments. The results revealed that excess dietary lipid supplements (more than 60 g/kg) would inhibit WG and would aggravate the lipid decomposition in the hepatopancreas. Based on WGR and FCR, the dietary lipid levels of 59.5 and 70.4 g/kg were optimal for growth performance and feed utilization of large-sized common carp.

Regulation of the epigenetic landscape by immune cell oxidants

Excessive production of microbicidal oxidants by neutrophils can damage host tissue. The short-term response of cells to oxidative stress is well understood, but the mechanisms behind long-term consequences require further clarification. Epigenetic pathways mediate cellular adaptation, and are therefore a potential target of oxidative stress. Indeed, there is evidence that many proteins and metabolites involved in epigenetic pathways are redox sensitive. In this review we provide an overview of the epigenetic landscape and discuss the potential for redox regulation. Using this information, we highlight specific examples where neutrophil oxidants react with epigenetic pathway components. We also use published data from redox proteomics to map out known intersections between oxidative stress and epigenetics that may signpost helpful directions for future investigation. Finally, we discuss the role neutrophils play in adaptive pathologies with a focus on tumour initiation and progression. We hope this information will stimulate further discourse on the emerging field of redox epigenomics.

The optimum dietary methionine requirement of juvenile humpback grouper (Cromileptes altivelis): effects on growth, micromorphology, protein and lipid metabolism

An 8-week feeding trial was conducted to evaluate optimum dietary methionine (Met) requirement of juvenile humpback grouper (Cromileptes altivelis) and the influence of dietary methionine (Met) supplementations on growth, gut micromorphology, protein and lipid metabolism. Seven isoproteic (48.91%) and isolipidic diets (10%) were made to contain 0.70, 0.88, 1.04, 1.27 1.46, 1.61 and 1.76% of dry matter Met levels. Results showed that lower survival, weight gain (WG%), protein efficiency ratio (PER), protein productive value (PPV) but higher daily feed intake (DFI) and feed conversion ratio (FCR) were observed in the Met deficient groups (0.70 and 0.88%). Optimum dietary Met requirement for humpback grouper was found to be 1.07% through the straight-broken line analysis of WG% against Met. Fish fed Met deficient diets (0.70, 0.88%) exhibited lower mRNA levels of growth hormone (GH), growth hormone receptor (GHR), insulin-like growth factor-I (IGF-1), target of rapamycin (TOR) as well as S6 kinase 1 (S6K1) than other dietary groups. Whereas, expression of genes related to general control nonderepressible (GCN2) kinase i.e., GCN2 and C/EBPβ enhancer-binding protein β was upregulated in fish fed low Met diets (P < 0.05). The mRNA expression of hepatic fatty acid synthase (FAS) and sterol regulatory element-binding protein-1 (SREBP-1) were higher in fish fed 0.70 and 0.88% dietary Met group and the lipolytic genes, hepatic peroxisome proliferator-activated receptor α (PPARα) and carnitine palmitoyl transferase-1 (CPT-1) showed an opposite variation tendency as FAS or SREBP1. Generally, the optimum Met requirement for humpback grouper was predicted to be 1.07% of dry matter.

Nutrition and Functions of Amino Acids in Fish

Aquaculture is increasingly important for providing humans with high-quality animal protein to improve growth, development and health. Farm-raised fish and shellfish now exceed captured fisheries for foods. More than 70% of the production cost is dependent on the supply of compound feeds. A public debate or concern over aquaculture is its environmental sustainability as many fish species have high requirements for dietary protein and fishmeal. Protein or amino acids (AAs), which are the major component of tissue growth, are generally the most expensive nutrients in animal production and, therefore, are crucial for aquatic feed development. There is compelling evidence that an adequate supply of both traditionally classified nutritionally essential amino acids (EAAs) and non-essential amino acids (NEAAs) in diets improve the growth, development and production performance of aquatic animals (e.g., larval metamorphosis). The processes for the utilization of dietary AAs or protein utilization by animals include digestion, absorption and metabolism. The digestibility and bioavailability of AAs should be carefully evaluated because feed production processes and AA degradation in the gut affect the amounts of dietary AAs that enter the blood circulation. Absorbed AAs are utilized for the syntheses of protein, peptides, AAs, and other metabolites (including nucleotides); biological oxidation and ATP production; gluconeogenesis and lipogenesis; and the regulation of acid-base balance, anti-oxidative reactions, and immune responses. Fish producers usually focus on the content or digestibility of dietary crude protein without considering the supply of AAs in the diet. In experiments involving dietary supplementation with AAs, inappropriate AAs (e.g., glycine and glutamate) are often used as the isonitrogenous control. At present, limited knowledge is available about either the cell- and tissue-specific metabolism of AAs or the effects of feed processing methods on the digestion and utilization of AAs in different fish species. These issues should be addressed to develop environment-friendly aquafeeds and reduce feed costs to sustain the global aquaculture.

Nutrient regulation of somatic growth in teleost fish. The interaction between somatic growth, feeding and metabolism

This review covers the current knowledge on the regulation of the somatic growth axis and its interaction with metabolism and feeding regulation. The main endocrine and neuroendocrine factors regulating both the growth axis and feeding behavior will be briefly summarized. Recently discovered neuropeptides and peptide hormones will be mentioned in relation to feeding control as well as growth hormone regulation. In addition, the influence of nutrient and nutrient sensing mechanisms on growth axis will be highlighted. We expect that in this process gaps of knowledge will be exposed, stimulating future research in those areas.

Effects of Partially Defatted Hermetia illucens Meal in Rainbow Trout Diet on Hepatic Methionine Metabolism

Simple Summary

For sustainable aquaculture development, fish meal from the sea in aquafeed should be replaced with other sustainable materials such as insect larvae. The authors fed black soldier fly maggot meal to rainbow trout and examined the expression of three genes and two metabolites involved in turn-over of methionine that is an essential amino acid in fish. According to the increase in the maggot content in the aquafeed, gene expression was modulated to maintain an optimal level of methionine metabolites. Dietary replacement of up to 50% of fish meal with the maggot meal was acceptable, implying future development of a new aquafeed for sustainable aquaculture.

Abstract

This study investigated, for the first time, the effects of replacement of fishmeal (FM) with insect meal from Hermetia illucens (HI) on the transcript levels of three genes involved in methionine (Met) metabolism in rainbow trout (Oncorhynchus mykiss) liver. Two target genes—betaine-homocysteine S-methyltransferase (BHMT) and S-adenosylhomocysteine hydrolase (SAHH)—are involved in Met resynthesis and the third one—cystathionine β synthase (CBS)—is involved in net Met loss (taurine synthesis). We also investigated the levels of two Met metabolites involved in the maintenance of methyl groups and homocysteine homeostasis in the hepatic tissue: S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). Three diets were formulated, an FM-based diet (HI0) and two diets in which 25% (HI25) and 50% (HI50) of FM was replaced with HI larvae meal. A 78-day feeding trial involved 360 rainbow trout with 178.9 ± 9.81 g initial average weight. Dietary replacement of up to 50% of FM with HI larvae meal, without any Met supplementation, did not negatively affect rainbow trout growth parameters and hepatic Met metabolism. In particular, Met availability from the insect-based diets directly modulated the transcript levels of two out of three target genes (CBS, SAHH) to maintain an optimal level of one-carbon metabolic substrates, i.e., the SAM:SAH ratio in the hepatic tissue.

dl-Methionine supplementation in a low-fishmeal diet affects the TOR/S6K pathway by stimulating ASCT2 amino acid transporter and insulin-like growth factor-I in the dorsal muscle of juvenile cobia (Rachycentron canadum)

An 8-week feeding experiment was conducted to investigate the effects of dl-methionine (Met) supplementation in a low-fishmeal diet on growth, key gene expressions of amino acid transporters and target of rapamycin (TOR) pathway in juvenile cobia, Rachycentron canadum. Seven isonitrogenous and isolipidic diets were formulated, containing 0·72, 0·90, 1·00, 1·24, 1·41, 1·63 and 1·86 % Met. Weight gain and specific growth rates increased gradually with Met levels of up to 1·24 % and then decreased gradually. In dorsal muscle, mRNA levels of ASCT2 in the 1·00 % Met group were significantly up-regulated compared with 0·72, 1·63, and 1·86 %. The insulin-like growth factor-I (IGF-I) mRNA levels in the dorsal muscle of fish fed 1·00 and 1·24 % Met were higher than those in fish fed other Met levels. In addition, fish fed 1·24 % Met showed the highest mRNA levels of TOR and phosphorylation of TOR on Ser2448. The phosphorylation of ribosomal p70-S6 kinase (S6K) on Ser371 in the dorsal muscle of fish fed 1·86 % Met was higher than those in the 0·72 % group. In conclusion, straight broken-line analysis of weight gain rate against dietary Met level indicates that the optimal Met requirement for juvenile cobia is 1·24 % (of DM, or 2·71 % dietary protein). Met supplementation in a low-fishmeal diet increased cobia growth via a mechanism that can partly be attributed to Met's ability to affect the TOR/S6K signalling pathway by enhancing ASCT2 and IGF-I transcription in cobia dorsal muscle.

Adequate supply of dietary taurine stimulates expression of molecular markers of growth and protein turnover in juvenile barramundi (Lates calcarifer)

A trial was conducted to investigate the effect of dietary taurine (Tau) supply on the plasma amino acid composition and hepatic expression of several genes in juvenile barramundi (Lates calcarifer) after feeding. Triplicate tanks of fish (average weight, 89.3 g) were fed diets containing either a deficient (1 g kg^-1), adequate (8 g kg^-1) or excessive (19 g kg^-1) level of dietary Tau. Liver tissues collected before feeding, and at 2- and 4-h post-feeding, were analysed for expression of genes involved in pathways of sulphur amino acid turnover, Tau biosynthesis and transport, target of rapamycin (TOR) signalling, the somatotropic axis and protein turnover. The treatment had no significant effect on the profiles of any amino acid in plasma collected over time after feeding, other than Tau and glycine. The expression profile of cystine and Tau synthetic genes suggested an effect of Tau excess on the metabolism of cystine. Markers of two pathways of Tau biosynthesis appear to be active in this species, providing proof that this species possesses the ability to synthesise Tau from SAA precursors. A marker for the regulation of Tau transport and homeostasis was shown to be directly regulated by Tau availability, whilst a link between adequate supply of Tau and TOR pathway-mediated growth stimulation was also apparent. An observed depression in expression of genes of the somatotropic axis, coupled with upregulation of the proteolytic and TOR-suppressing genes, in response to excessive Tau supply in the diet, signalled that excessive Tau may not be conducive to optimal growth in this species.

Environmental hypoxia causes growth retardation, osteoclast differentiation and calcium dyshomeostasis in juvenile rainbow trout (Oncorhynchus mykiss)

Hypoxia generally refers to a dissolved oxygen (DO) level that is less than 2-3 mg/L. With ongoing global warming and environment pollution, environmental or geological studies showed hypoxia frequently occurs in global aquatic systems including ocean, river, estuaries and coasts. A preliminary study was performed to evaluate hypoxia tolerant of rainbow trout (Oncorhynchus mykiss) with parameters of mortality, behavior, endocrine and metabolite, identifying three DO levels including normoxia (Ctrl, 7.0 mg/L), non-lethal hypoxia (NH, 4.5 mg/L) and lethal hypoxia (LH, 3.0 mg/L). Furthermore, trout was treated by Ctrl, NH and LH for six hours to mimic the acute hypoxia in wild and/or farming conditions. A significantly higher mortality was observed in LH group. Trout of NH and LH showed stressful responses with unnormal swimming, increased serum cortisol and up-regulated gill hif1α transcription. Despite trout of NH and LH increased the oxygen delivery abilities by increasing the serum hemoglobin levels, the anerobic metabolism were inevitably observed with increased lactate. This study also showed a prolonged influence of NH and LH on growth after 30-days' recovery. Based on RNA-Seq data, different expression genes (DEGs) associated with stress, apoptosis, antioxidant, chaperone, growth, calcium and vitamin D metabolism were identified. Enrichment analysis showed DEGs were clustered in osteoclast differentiation, apoptosis and intracellular signaling transduction pathways. Results further showed NH and LH significantly decreased bone calcium content and disrupted the growth hormone-insulin-like growth factor (GH-IGF) axis. Our study might contribute to a better understanding of the effects of hypoxia on rainbow trout.

Characterization of the immune roles of cathepsin L in turbot (Scophthalmus maximus L.) mucosal immunity

Cathepsin L (CTSL) is one of the crucial enzymes in cathepsin family, which has been widely known for its involvement in the innate immunity. However, it still remains poorly understood how CTSL modulates the immune system of teleosts. In this study, we captured three cathepsin L genes (SmCTSL, SmCTSL.1 and SmCTSL1) from turbot (Scophthalmus maximus). The coding sequences of SmCTSL, SmCTSL.1 and SmCTSL1 are 1,026 bp, 1,005 bp and 1,017 bp in length and encode 341, 334 and 338 amino acids, respectively. In details, transcripts of CTSL genes share same domains as other CTSL genes, one signal peptide, one propeptide and one papain family cysteine protease domain. Protein interaction network analysis indicated that turbot CTSL genes may play important roles in apoptotic signaling and involve in innate immune response. Evidence from subcellular localization demonstrated that the three Cathepsin L proteins were ubiquitous in nucleus and cytoplasm. The cathepsin L genes were widely expressed in all the tested tissues with the highest expression level of SmCTSL in spleen, and SmCTSL.1 and SmCTSL1 in intestine. Following Vibrio anguillarum, Edwardsiella tarda and Streptococcus iniae challenge, these cathepsin L genes were significantly regulated in mucosal tissues in all the challenges, especially significant down-regulation occurred rapidly in intestine in all the three challenges. In addition, the three cathepsin L genes showed strong binding ability to all the examined microbial ligands (LPS, PGN and LTA). Further studies should be used to analyze the specific function of these three cathepsin L genes. By then, we can use their function to maintain the integrity of the mucosal barrier, thereby promoting the disease resistance line and family selection in turbot.

Glucose regulates protein turnover and growth-related mechanisms in rainbow trout myogenic precursor cells

Rainbow trout are considered glucose intolerant because they are poor utilizers of glucose, despite having functional insulin receptors and glucose transporters. Following high carbohydrate meals, rainbow trout are persistently hyperglycemic, which is likely due to low glucose utilization in peripheral tissues including the muscle. Also, rainbow trout myogenic precursor cells (MPCs) treated in vitro with insulin and IGF1 increase glucose uptake and protein synthesis, whereas protein degradation is decreased. Given our understanding of glucose regulation in trout, we sought to understand how glucose concentrations affect protein synthesis, protein degradation; and expression of genes associated with muscle growth and proteolysis in MPCs. We found that following 24 h and 48 h of treatment with low glucose media (5.6 mM), myoblasts had significant decreases in protein synthesis. Also, low glucose treatments affected the expression of both mstn2a and igfbp5. These findings support that glucose is a direct regulator of protein synthesis and growth-related mechanisms in rainbow trout muscle.

The anorectic effect of central PYY1-36 treatment in rainbow trout (Oncorhynchus mykiss) is associated with changes in mRNAs encoding neuropeptides and parameters related to fatty acid sensing and metabolism

We hypothesized that peptide YY (PYY) is involved in the metabolic regulation of food intake in fish. Therefore, we assessed in rainbow trout (Oncorhynchus mykiss) the effects of intracerebroventricular treatment with 10 ng/g PYY_1-36 on food intake, expression of neuropeptides involved in food intake control, and the activity of fatty acid-sensing systems. The administration of PYY_1-36 caused a significant reduction in food intake up to 24 h post-treatment. This anorectic action was associated with changes 2 h after treatment in mRNA abundance of neuropeptides involved in metabolic regulation of food intake in hypothalamus (decreased NPY and raised CART values) and hindbrain (increased POMCa1 values). We also observed that PYY_1-36 treatment induced changes in mRNA abundance of parameters related to fatty acid sensing and metabolism in hypothalamus (decreased values of ACLY, PPARγ, and SREBP1c) and hindbrain (increased values of LPL, FAT/CD36, PPARα, PPARγ, and SREBP1c and decreased values of UCP2a). PYY_1-36 treatment also increased mRNA abundance of mTOR. In general, it seems that mRNAs encoding some components of the machinery required for fatty acid sensing and metabolism are activated by PYY_1-36. The response observed was higher in the hindbrain than in the hypothalamus, supporting the greater importance of this brain area in mediating the modulatory effects of gastrointestinal hormones on feeding regulation.

Lysine supplement benefits the growth performance, protein synthesis, and muscle development of Megalobrama amblycephala fed diets with fish meal replaced by rice protein concentrate

This study aimed to investigate the effects of lysine supplement on the growth performance of blunt snout bream Megalobrama amblycephala fed diets with fish meal (FM) replaced by rice protein concentrate (RPC) with the potential mechanisms characterized. Fish were fed three diets, including the FM diet (containing FM), the RPC diet (FM replaced by RPC), and the MRPC diet (the RPC diet supplemented with lysine) for 8 weeks. Weight gain, protein efficiency ratio, and nitrogen and energy utilization of fish fed the FM diet were all significantly higher than those of the RPC treatment, but they showed no statistical difference with those of the MRPC group. Fish fed the RPC diet showed shorter villi length of the distal intestine than that of the other treatments. No significance was found in whole-body composition and intestinal and hepatic cell proliferation among all the treatments. However, fish fed the RPC diet obtained relatively low transcriptions of growth hormone (GH), GH receptor, insulin-like growth factor-I (IGF-I), target of rapamycin (TOR), ribosomal protein S6 kinase 1, myoblast determination protein, myogenic factor 5, and myostatin a (MSTNa) but high levels of eukaryotic translation initiation factor 4E-binding protein 2 (4E-BP2) than those of the other groups. Furthermore, little difference was found in the transcriptions of 4E-BP2, myogenin, muscle-specific regulatory 4, and MSTNb in muscle. Overall, these results showed that dietary supplement of lysine benefits the growth performance of blunt snout bream fed FM-free diets through the mediation of the GH-IGF-I axis, TOR signaling pathway, myogenic regulatory factors, and MSTN.

Lysine and methionine supplementation ameliorates high inclusion of soybean meal inducing intestinal oxidative injury and digestive and antioxidant capacity decrease of yellow catfish

The yellow catfish Pelteobagrus fulvidraco with initial average weight 16.6 ± 0.17 g were fed three extruded diets for 56 days. Fish meal (FM) diet was formulated as the normal control with 380 g FM and 200 g soybean meal (SBM) kg-1 diet. The SBM diet was prepared with 220 g FM and 360 g SBM kg-1 diet without Lys or Met supplementation. The SBM supplement (SBMS) diet was similar to SBM diet and supplemented with Lys and Met to ensure their levels similar to FM diet. The results showed fish fed SBM diet had lower percent weight gain and specific growth rate than the other two groups (P < 0.05). Whole body protein content of fish fed FM and SBMS diets were higher than that of fish fed SBM diet (P < 0.05). The hepatosomatic and intestosomatic indexes of fish fed SBM diet were significantly lower than that of fish fed FM and SBMS diets (P < 0.05). The activities of pepsin in stomach, trypsin, and chymotrypsin in intestine, alkaline phosphatase and creatine kinase in proximal intestine, Na+, K+-ATPase, and gamma-glutamyl transpeptidase in distal intestine were significantly higher in fish fed FM and SBMS diets compared to SBM diet. The activities of catalase, glutathione-S-transferase, reduced glutathione, superoxide anion scavenging, and hydroxyl radical scavenging in the intestine showed the same changes (P < 0.05). Malondialdehyde and protein carbonyl contents in intestine were significantly decreased in fish fed SBMS diet compared to SBM diet. These results indicated high inclusion of SBM induced intestinal oxidative injury and digestive and antioxidant capacity decrease. The Lys and Met supplementation could ameliorate these adverse effects on yellow catfish.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.

Insulin-Like Growth Factor-Binding Proteins of Teleost Fishes

The insulin-like growth factor (Igf) binding protein (Igfbp) family has a broad range of physiological functions and a fascinating evolutionary history. This review focuses on the Igfbps of teleost fishes, where genome duplication events have diversified gene repertoire, function, and physiological regulation-with six core Igfbps expanded into a family of over twenty genes in some lineages. In addition to briefly summarizing the current state of knowledge on teleost Igfbp evolution, function, and expression-level regulation, we highlight gaps in our understanding and promising areas for future work.

Hypothalamic mechanisms linking fatty acid sensing and food intake regulation in rainbow trout

We assessed in rainbow trout hypothalamus the effects of oleate and octanoate on levels and phosphorylation status of two transcription factors, FoxO1 and CREB, possibly involved in linking activation of fatty acid sensing with modulation of food intake through the expression of brain neuropeptides. Moreover, we assessed changes in the phosphorylation status of three proteins possibly involved in modulation of these transcription factors such as Akt, AMPK and mTOR. In a first experiment, we evaluated, in pools of hypothalamus incubated for 3 h and 6 h at 15°C in a modified Hanks' medium containing 100 or 500 µM oleate or octanoate, the response of fatty acid sensing, neuropeptide expression and phosphorylation status of proteins of interest. The activation of fatty acid sensing and enhanced anorectic potential occurred in parallel with the activation of Akt and mTOR, and the inhibition of AMPK. The changes in these proteins would relate to a neuropeptide expression through changes in the phosphorylation status of transcription factors under their control, such as CREB and FoxO1, which displayed inhibitory (CREB) or activatory (FoxO1) responses when tissues were incubated with oleate or octanoate. In a second experiment, we incubated hypothalamus for 6 h with 500 µM oleate or octanoate alone or in the presence of specific inhibitors of Akt, AMPK, mTOR, CREB or FoxO1. The presence of inhibitors counteracted the effects of oleate or octanoate on the phosphorylation status of the proteins of interest. The results support, for the first time in fish, the involvement of these proteins in the regulation of food intake by fatty acids.

Role of methionine on epigenetic modification of DNA methylation and gene expression in animals

DNA methylation is one of the main epigenetic phenomena affecting gene expression. It is an important mechanism for the development of embryo, growth and health of animals. As a key nutritional factor limiting the synthesis of protein, methionine serves as the precursor of S-adenosylmethionine (SAM) in the hepatic one-carbon metabolism. The dietary fluctuation of methionine content can alter the levels of metabolic substrates in one-carbon metabolism, e.g., the SAM, S-adenosylhomocysteine (SAH), and change the expression of genes related to the growth and health of animals by DNA methylation reactions. The ratio of SAM to SAH is called ‘methylation index’ but it should be carefully explained because the complexity of methylation reaction. Alterations of methylation in a specific cytosine-guanine (CpG) site, rather than the whole promoter region, might be enough to change gene expression. Aberrant methionine cycle may provoke molecular changes of one-carbon metabolism that results in deregulation of cellular hemostasis and health problems. The importance of DNA methylation has been underscored but the mechanisms of methionine affecting DNA methylation are poorly understood. Nutritional epigenomics provides a promising insight into the targeting epigenetic changes in animals from a nutritional standpoint, which will deepen and expand our understanding of genes, molecules, tissues, and animals in which methionine alteration influences DNA methylation and gene expression.

Ceramide counteracts the effects of ghrelin on the metabolic control of food intake in rainbow trout

In mammals, ceramides are involved in the modulation of the orexigenic effects of ghrelin (GHRL). We previously demonstrated in rainbow trout that intracerebroventricular (ICV) treatment with ceramide (2.5 µg/100 g fish) resulted in an anorexigenic response, i.e. a response opposed to that described in mammals, where ceramide treatment is orexigenic. Therefore, we hypothesized that the putative interaction between GHRL and ceramide must be different in fish. Accordingly, in a first experiment, we observed that ceramide levels in the hypothalamus of rainbow trout did not change after ICV treatment with GHRL. In a second experiment, we assessed whether the effects of GHRL treatment on the regulation of food intake in rainbow trout changed in the presence of ceramide. Thus, we injected ICV GHRL and ceramide alone or in combination to evaluate in hypothalamus and hindbrain changes in parameters related to the metabolic control of food intake. The presence of ceramide generally counteracted the effects elicited by GHRL on fatty acid-sensing systems, the capacity of integrative sensors (AMPK, mTOR and SIRT-1), proteins involved in cellular signalling pathways (Akt and FoxO1) and neuropeptides involved in the regulation of food intake (AgRP, NPY, POMC and CART). The results are discussed in the context of regulation of food intake by metabolic and endocrine inputs.

Uncommon functional properties of the first piscine 26S proteasome from the Antarctic notothenioid Trematomus bernacchii

The antioxidant defense mechanisms have a great impact on the life of Antarctic organisms. The present study could represent the first evidence of a direct involvement of the 26S proteasome in the antioxidant defense systems of fish adapted to cold.

Protein homoeostasis is a fundamental process allowing the preservation of functional proteins and it has a great impact on the life of the Antarctic organisms. However, the effect of low temperatures on protein turnover is poorly understood and the cold-adaptation of the degradation machinery remains an unresolved issue. As the 26S proteasome represents the main proteolytic system devoted to the controlled degradation of intracellular proteins, the purpose of the present study was to investigate the functions of this complex in the notothenioid Trematomus bernacchii, in order to better understand its role in the physiology of Antarctic fish. To this aim, we purified and characterized the 26S proteasome from T. bernacchii and isolated the cDNAs codifying seven of the 14 subunits belonging to the proteasome 20S core particle. Results provided evidences of the high resistance of the piscine 26S proteasome to oxidative agents and of its ‘uncommon’ ability to efficiently hydrolyse oxidized bovine serum albumin (BSA), suggesting that this enzymatic complex could play a key role in the antioxidant defense systems in fish inhabiting permanently cold marine environments. These unique properties were also reflected by the 3D model analysis, which revealed a higher structural stability of the piscine complex respect to the murine template. Finally, a comparative analysis, performed in a variety of tissues collected from T. bernacchii and the temperate fish Dicentrarchus labrax, showed a lower protein retention in the cold-adapted fish, possibly due to a better efficiency of its degradation machinery.

Lysine and Leucine Deficiencies Affect Myocytes Development and IGF Signaling in Gilthead Sea Bream (Sparus aurata)

Optimizing aquaculture production requires better knowledge of growth regulation and improvement in diet formulation. A great effort has been made to replace fish meal for plant protein sources in aquafeeds, making necessary the supplementation of such diets with crystalline amino acids (AA) to cover the nutritional requirements of each species. Lysine and Leucine are limiting essential AA in fish, and it has been demonstrated that supplementation with them improves growth in different species. However, the specific effects of AA deficiencies in myogenesis are completely unknown and have only been studied at the level of hepatic metabolism. It is well-known that the TOR pathway integrates the nutritional and hormonal signals to regulate protein synthesis and cell proliferation, to finally control muscle growth, a process also coordinated by the expression of myogenic regulatory factors (MRFs). This study aimed to provide new information on the impact of Lysine and Leucine deficiencies in gilthead sea bream cultured myocytes examining their development and the response of insulin-like growth factors (IGFs), MRFs, as well as key molecules involved in muscle growth regulation like TOR. Leucine deficiency did not cause significant differences in most of the molecules analyzed, whereas Lysine deficiency appeared crucial in IGFs regulation, decreasing significantly IGF-I, IGF-II and IGF-IRb mRNA levels. This treatment also down-regulated the gene expression of different MRFs, including Myf5, Myogenin and MyoD2. These changes were also corroborated by a significant decrease in proliferation and differentiation markers in the Lysine-deficient treatment. Moreover, both Lysine and Leucine limitation induced a significant down-regulation in FOXO3 gene expression, which deserves further investigation. We believe that these results will be relevant for the production of a species as appreciated for human consumption as it is gilthead sea bream and demonstrates the importance of an adequate level of Lysine in fishmeal diet formulation for optimum growth.

Mucosal expression signatures of two Cathepsin L in channel catfish (Ictalurus punctatus) following bacterial challenge

The mucosal surfaces of fish are the first line of host defense against various pathogens. The mucosal immune responses are the most critical events to prevent pathogen attachment and invasion. Cathepsins are a group of peptidases that involved in different levels of immune responses, but the knowledge of the roles of Cathepsin in mucosal immune responses against bacterial infection are still lacking. Therefore, in the present study we characterized the Cathepsin L gene family in channel catfish, and profiled their expression levels after challenging with two different Gram-negative bacterial pathogens. Here, two Cathepsin L genes were identified from channel catfish and were designated CTSL1a and CTSL.1. Comparing to other fish species, the catfish CTSL genes are highly conserved in their structural features. Phylogenetic analysis was conducted to confirm the identification of CTSL genes. Expression analysis revealed that the CTSL genes were ubiquitously expressed in all tested tissues. Following infection, the CTSL genes were significantly induced at most timepoints in mucosal tissues. But the expression patterns varied depending on both pathogen and tissue types, suggesting that CTSL genes may exert disparate functions or exhibit distinct tissue-selective roles in mucosal immune responses. Our findings here, clearly revealed the key roles of CTSL in catfish mucosal immunity; however, further studies are needed to expand functional characterization and examine whether CTSL may also play additional physiological roles in catfish mucosal tissues.