IGF-I and amino acids effects through TOR signaling on proliferation and differentiation of gilthead sea bream cultured myocytes

Chaperone-mediated autophagy protects against hyperglycemic stress

Chaperone-mediated autophagy (CMA) is a major pathway of lysosomal proteolysis critical for cellular homeostasis and metabolism, and whose defects have been associated with several human pathologies. While CMA has been well described in mammals, functional evidence has only recently been documented in fish, opening up new perspectives to tackle this function under a novel angle. Now we propose to explore CMA functions in the rainbow trout (RT, Oncorhynchus mykiss), a fish species recognized as a model organism of glucose intolerance and characterized by the presence of two paralogs of the CMA-limiting factor Lamp2A (lysosomal associated membrane protein 2A). To this end, we validated a fluorescent reporter (KFERQ-PA-mCherry1) previously used to track functional CMA in mammalian cells, in an RT hepatoma-derived cell line (RTH-149). We found that incubation of cells with high-glucose levels (HG, 25 mM) induced translocation of the CMA reporter to lysosomes and/or late endosomes in a KFERQ- and Lamp2A-dependent manner, as well as reduced its half-life compared to the control (5 mM), thus demonstrating increased CMA flux. Furthermore, we observed that activation of CMA upon HG exposure was mediated by generation of mitochondrial reactive oxygen species, and involving the antioxidant transcription factor Nfe2l2/Nrf2 (nfe2 like bZIP transcription factor 2). Finally, we demonstrated that CMA plays an important protective role against HG-induced stress, primarily mediated by one of the two RT Lamp2As. Together, our results provide unequivocal evidence for CMA activity existence in RT and highlight both the role and regulation of CMA during glucose-related metabolic disorders.Abbreviations: AREs: antioxidant response elements; CHC: α-cyano -4-hydroxycinnamic acid; Chr: chromosome; CMA: chaperone-mediated autophagy; CT: control; DMF: dimethyl fumarate; Emi: endosomal microautophagy; HG: high-glucose; HMOX1: heme oxygenase 1; H2O2: hydrogen peroxide; KFERQ: lysine-phenylalanine-glutamate-arginine-glutamine; LAMP1: lysosomal associated membrane protein 1; LAMP2A: lysosomal associated membrane protein 2A; MCC: Manders' correlation coefficient; Manders' correlation coefficient Mo: morpholino oligonucleotide; NAC: N-acetyl cysteine; NFE2L2/NRF2: NFE2 like bZIP transcription factor 2; PA-mCherry: photoactivable mCherry; PCC: Pearson's correlation coefficient; ROS: reactive oxygen species; RT: rainbow trout; siRNAs: small interfering RNAs; SOD: superoxide dismutase; Tsg101: tumor susceptibility 101; TTFA: 2-thenoyltrifluoroacetone; WGD: whole-genome duplication.

Cysteamine improves growth and the GH/IGF axis in gilthead sea bream (Sparus aurata): in vivo and in vitro approaches

Aquaculture is the fastest-growing food production sector and nowadays provides more food than extractive fishing. Studies focused on the understanding of how teleost growth is regulated are essential to improve fish production. Cysteamine (CSH) is a novel feed additive that can improve growth through the modulation of the GH/IGF axis; however, the underlying mechanisms and the interaction between tissues are not well understood. This study aimed to investigate the effects of CSH inclusion in diets at 1.65 g/kg of feed for 9 weeks and 1.65 g/kg or 3.3 g/kg for 9 weeks more, on growth performance and the GH/IGF-1 axis in plasma, liver, stomach, and white muscle in gilthead sea bream (Sparus aurata) fingerlings (1.8 ± 0.03 g) and juveniles (14.46 ± 0.68 g). Additionally, the effects of CSH stimulation in primary cultured muscle cells for 4 days on cell viability and GH/IGF axis relative gene expression were evaluated. Results showed that CSH-1.65 improved growth performance by 16% and 26.7% after 9 and 18 weeks, respectively, while CSH-3.3 improved 32.3% after 18 weeks compared to control diet (0 g/kg). However, no significant differences were found between both experimental doses. CSH reduced the plasma levels of GH after 18 weeks and increased the IGF-1 ones after 9 and 18 weeks. Gene expression analysis revealed a significant upregulation of the ghr-1, different igf-1 splice variants, igf-2 and the downregulation of the igf-1ra and b, depending on the tissue and dose. Myocytes stimulated with 200 µM of CSH showed higher cell viability and mRNA levels of ghr1, igf-1b, igf-2 and igf-1rb compared to control (0 µM) in a similar way to white muscle. Overall, CSH improves growth and modulates the GH/IGF-1 axis in vivo and in vitro toward an anabolic status through different synergic ways, revealing CSH as a feasible candidate to be included in fish feed.

Fish waste to sustainable additives: Fish protein hydrolysates alleviate intestinal dysbiosis and muscle atrophy induced by poultry by-product meal in Lates calcarifer juvenile

Valorising waste from the processing of fishery and aquaculture products into functional additives, and subsequent use in aquafeed as supplements could be a novel approach to promoting sustainability in the aquaculture industry. The present study supplemented 10% of various fish protein hydrolysates (FPHs), obtained from the hydrolysis of kingfish (KH), carp (CH) and tuna (TH) waste, with 90% of poultry by-product meal (PBM) protein to replace fishmeal (FM) completely from the barramundi diet. At the end of the trial, intestinal mucosal barriers damage, quantified by villus area (VA), lamina propria area (LPA), LPA ratio, villus length (VL), villus width (VW), and neutral mucin (NM) in barramundi fed a PBM-based diet was repaired when PBM was supplemented with various FPHs (p < 0.05, 0.01, and 0.001). PBM-TH diet further improved these barrier functions in the intestine of fish (p < 0.05 and 0.001). Similarly, FPHs supplementation suppressed PBM-induced intestinal inflammation by controlling the expression of inflammatory cytokines (tnf-α and il-10; p < 0.05 and 0.001) and a mucin-relevant production gene (i-mucin c; p < 0.001). The 16S rRNA data showed that a PBM-based diet resulted in dysbiosis of intestinal bacteria, supported by a lower abundance of microbial diversity (p < 0.001) aligned with a prevalence of Photobacterium. PBM-FPHs restored intestine homeostasis by enhancing microbial diversity compared to those fed a PBM diet (p < 0.001). PBM-TH improved the diversity (p < 0.001) further by elevating the Firmicutes phylum and the Ruminococcus, Faecalibacterium, and Bacteroides genera. Muscle atrophy, evaluated by fiber density, hyperplasia and hypertrophy and associated genes (igf-1, myf5, and myog), occurred in barramundi fed PBM diet but was repaired after supplementation of FPHs with the PBM (p < 0.05, 0.01, and 0.001). Similarly, creatine kinase, calcium, phosphorous, and haptoglobin were impacted by PBM-based diet (p < 0.05) but were restored in barramundi fed FPHs supplemented diets (p < 0.05 and 0.01). Hence, using circular economy principles, functional FPHs could be recovered from the fish waste applied in aquafeed formulations and could prevent PBM-induced intestinal dysbiosis and muscular atrophy.

GRAPHICAL ABSTRACT

Muscle regeneration in gilthead sea bream: Implications of endocrine and local regulatory factors and the crosstalk with bone

Fish muscle regeneration is still a poorly known process. In the present study, an injury was done into the left anterior epaxial skeletal muscle of seventy 15 g gilthead sea bream (Sparus aurata) juveniles to evaluate at days 0, 1, 2, 4, 8, 16 and 30 post-wound, the expression of several muscle genes. Moreover, transcripts' expression in the bone (uninjured tissue) was also analyzed. Histology of the muscle showed the presence of dead tissue the first day after injury and how the damaged fibers were removed and replaced by new muscle fibers by day 16 that kept growing up to day 30. Gene expression results showed in muscle an early upregulation of igf-2 and a downregulation of ghr-1 and igf-1. Proteolytic systems expression increased with capn2 and ctsl peaking at 1 and 2 days post-injury, respectively and mafbx at day 8. A pattern of expression that fitted well with active myogenesis progression 16 days after the injury was then observed, with the recovery of igf-1, pax7, cmet, and cav1 expression; and later on, that of cav3 as well. Furthermore, the first days post-injury, the cytokines il-6 and il-15 were also upregulated confirming the tissue inflammation, while tnfα was only upregulated at days 16 and 30 to induce satellite cells recruitment; overall suggesting a possible role for these molecules as myokines. The results of the bone transcripts showed an upregulation first, of bmp2 and ctsk at days 1 and 2, respectively; then, ogn1 and ocn peaked at day 4 in parallel to mstn2 downregulation, and runx2 and ogn2 increased after 8 days of muscle injury, suggesting a possible tissue crosstalk during the regenerative process. Overall, the present model allows studying the sequential involvement of different regulatory molecules during muscle regeneration, as well as the potential relationship between muscle and other tissues such as bone to control musculoskeletal development and growth, pointing out an interesting new line of research in this group of vertebrates.

Gilthead Seabream Liver Integrative Proteomics and Metabolomics Analysis Reveals Regulation by Different Prosurvival Pathways in the Metabolic Adaptation to Stress

The study of the molecular mechanisms of stress appraisal on farmed fish is paramount to ensuring a sustainable aquaculture. Stress exposure can either culminate in the organism's adaptation or aggravate into a metabolic shutdown, characterized by irreversible cellular damage and deleterious effects on fish performance, welfare, and survival. Multiomics can improve our understanding of the complex stressed phenotype in fish and the molecular mediators that regulate the underlying processes of the molecular stress response. We profiled the stress proteome and metabolome of Sparus aurata responding to different challenges common to aquaculture production, characterizing the disturbed pathways in the fish liver, i.e., the central organ in mounting the stress response. Label-free shotgun proteomics and untargeted metabolomics analyses identified 1738 proteins and 120 metabolites, separately. Mass spectrometry data have been made fully accessible via ProteomeXchange, with the identifier PXD036392, and via MetaboLights, with the identifier MTBLS5940. Integrative multivariate statistical analysis, performed with data integration analysis for biomarker discovery using latent components (DIABLO), depicted the 10 most-relevant features. Functional analysis of these selected features revealed an intricate network of regulatory components, modulating different signaling pathways related to cellular stress, e.g., the mTORC1 pathway, the unfolded protein response, endocytosis, and autophagy to different extents according to the stress nature. These results shed light on the dynamics and extent of this species' metabolic reprogramming under chronic stress, supporting future studies on stress markers' discovery and fish welfare research.

A continuous myofibroblast precursor cell line from the tail muscle of Australasian snapper (Chrysophrys auratus) that responds to transforming growth factor beta and fibroblast growth factor

Chrysophrys auratus (Australasian snapper) is one of the largest and most valuable finfish from capture fisheries in New Zealand, yet no cell lines from this species are reported in the scientific literature. Here, we describe a muscle-derived cell line initiated from the tail of a juvenile snapper which has been designated CAtmus1PFR (Chrysophrys auratus, tail muscle, Plant & Food Research). The cell line has been passaged over 100 times in 3 years and is considered immortal. Cells are reliant on serum supplementation for proliferation and exhibit a broad thermal profile comparable to the eurythermic nature of C. auratus in vivo. The impact of exogenous growth factors, including insulin-like growth factors I and II (IGF-I and IGF-II), basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGFβ), on cell morphology and proliferation was investigated. Insulin-like growth factors acted as mitogens and had minimal effect on cell morphology. TGFβ exposure resulted in CAtmus1PFR exhibiting a myofibroblast morphology becoming enlarged with actin bundling. This differentiation was confirmed through the expression of smooth muscle actin (sma), an increase in type 1 collagen (col1a) expression, and a loss of motility. Expression of col1a and sma was decreased when cells were exposed to bFGF, and no actin bundling was observed. These data indicate that CAtmus1PFR may be myofibroblastic precursor cells descending from mesenchymal progenitor cells present in the tail muscle myosepta.

Myomaker and Myomixer Characterization in Gilthead Sea Bream under Different Myogenesis Conditions

Skeletal muscle is formed by multinucleated myofibers originated by waves of hyperplasia and hypertrophy during myogenesis. Tissue damage triggers a regeneration process including new myogenesis and muscular remodeling. During myogenesis, the fusion of myoblasts is a key step that requires different genes' expression, including the fusogens myomaker and myomixer. The present work aimed to characterize these proteins in gilthead sea bream and their possible role in in vitro myogenesis, at different fish ages and during muscle regeneration after induced tissue injury. Myomaker is a transmembrane protein highly conserved among vertebrates, whereas Myomixer is a micropeptide that is moderately conserved. myomaker expression is restricted to skeletal muscle, while the expression of myomixer is more ubiquitous. In primary myocytes culture, myomaker and myomixer expression peaked at day 6 and day 8, respectively. During regeneration, the expression of both fusogens and all the myogenic regulatory factors showed a peak after 16 days post-injury. Moreover, myomaker and myomixer were present at different ages, but in fingerlings there were significantly higher transcript levels than in juveniles or adult fish. Overall, Myomaker and Myomixer are valuable markers of muscle growth that together with other regulatory molecules can provide a deeper understanding of myogenesis regulation in fish.

Hydroxytyrosol-rich extract from olive juice as an additive in gilthead sea bream juveniles fed a high-fat diet: Regulation of somatic growth

The dietary inclusion of plant-based products in fish feeds formulation is required for the sustainable development of aquaculture. Moreover, considering functional diets, hydroxytyrosol, one of the major phenolic compounds found in olives (Olea europaea), has been identified as a potential candidate to be used in the aquafeeds industry due to its health promoting abilities. The aim of this study was to evaluate the effects of the inclusion of an olive juice extract rich in hydroxytyrosol as an additive (0.52 g HT/kg feed) in a high-fat (24% lipids) diet in gilthead sea bream (Sparus aurata) juveniles. Moreover, the experimental diets, with or without the extract, were administered daily at a standard (3% of total biomass in the tank) or restricted ration (40% reduction) for 8–9 weeks. Growth and biometric parameters, insulin-like growth factor 1 (IGF-1) plasma levels and growth hormone/IGF axis-, myogenic- and osteogenic-related genes expression in liver, white muscle and/or bone were analyzed. Moreover, in vitro cultures of vertebra bone-derived cells from fish fed the diets at a standard ration were performed at weeks 3 and 9 to explore the effects of hydroxytyrosol on osteoblasts development. Although neither body weight or any other biometric parameter were affected by diet composition after 4 or 8 weeks, the addition of the hydroxytyrosol-rich extract to the diet increased IGF-1 plasma levels, regardless of the ration regime, suggesting an anabolic condition. In muscle, the higher mRNA levels of the binding protein igfbp-5b and the myoblast fusion marker dock5 in fish fed with the hydroxytyrosol-rich diet suggested that this compound may have a role in muscle, inducing development and a better muscular condition. Furthermore in bone, increased osteogenic potential while delayed matrix mineralization after addition to the diet of the olive juice extract was supported by the upregulated expression of igf-1 and bmp4 and reduced transcript levels of osteopontin. Overall, this study provides new insights into the beneficial use of hydroxytyrosol as a dietary additive in gilthead sea bream functional diets to improve muscle-skeletal condition and, the aquaculture industry.

Effects of dietary tryptophan on muscle growth, protein synthesis and antioxidant capacity in hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂

The present study evaluated effects of dietary supplementation with tryptophan (Trp) on muscle growth, protein synthesis and antioxidant capacity in hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂. Fish were fed six different diets containing 2·6 (control), 3·1, 3·7, 4·2, 4·7 and 5·6 g Trp/kg diet for 56 d, respectively. Results showed that dietary Trp significantly (1) improved muscle protein content, fibre density and frequency of fibre diameter; (2) up-regulated the mRNA levels of PCNA, myf5, MyoD1, MyoG, MRF4, IGF-I, IGF-II, IGF-IR, PIK3Ca, TOR, 4EBP1 and S6K1; (3) increased phosphorylation levels of AKT, TOR and S6K1; (4) decreased contents of MDA and PC, and increased activities of CAT, GST, GR, ASA and AHR; (5) up-regulated mRNA levels of CuZnSOD, CAT, GST, GPx, GCLC and Nrf2, and decreased Keap1 mRNA level; (6) increased nuclear Nrf2 protein level and the intranuclear antioxidant response element-binding ability, and reduced Keap1 protein level. These results indicated that dietary Trp improved muscle growth, protein synthesis as well as antioxidant capacity, which might be partly related to myogenic regulatory factors, IGF/PIK3Ca/AKT/TOR and Keap1/Nrf2 signalling pathways. Finally, based on the quadratic regression analysis of muscle protein and MDA contents, the optimal Trp requirements of hybrid catfish (21·82-39·64 g) were estimated to be 3·94 and 3·93 g Trp/kg diet (9·57 and 9·54 g/kg of dietary protein), respectively.

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.

An insight on the impact of teleost whole genome duplication on the regulation of the molecular networks controlling skeletal muscle growth

Fish muscle growth is a complex process regulated by multiple pathways, resulting on the net accumulation of proteins and the activation of myogenic progenitor cells. Around 350–320 million years ago, teleost fish went through a specific whole genome duplication (WGD) that expanded the existent gene repertoire. Duplicated genes can be retained by different molecular mechanisms such as subfunctionalization, neofunctionalization or redundancy, each one with different functional implications. While the great majority of ohnolog genes have been identified in the teleost genomes, the effect of gene duplication in the fish physiology is still not well characterized. In the present study we studied the effect of WGD on the transcription of the duplicated components controlling muscle growth. We compared the expression of lineage-specific ohnologs related to myogenesis and protein balance in the fast-skeletal muscle of pacus (Piaractus mesopotamicus—Ostariophysi) and Nile tilapias (Oreochromis niloticus—Acanthopterygii) fasted for 4 days and refed for 3 days. We studied the expression of 20 ohnologs and found that in the great majority of cases, duplicated genes had similar expression profiles in response to fasting and refeeding, indicating that their functions during growth have been conserved during the period after the WGD. Our results suggest that redundancy might play a more important role in the retention of ohnologs of regulatory pathways than initially thought. Also, comparison to non-duplicated orthologs showed that it might not be uncommon for the duplicated genes to gain or loss new regulatory elements simultaneously. Overall, several of duplicated ohnologs have similar transcription profiles in response to pro-growth signals suggesting that evolution tends to conserve ohnolog regulation during muscle development and that in the majority of ohnologs related to muscle growth their functions might be very similar.

Ascorbic Acid Supplementation Improves Skeletal Muscle Growth in Pacu (Piaractus mesopotamicus) Juveniles: In Vivo and In Vitro Studies

In fish, fasting leads to loss of muscle mass. This condition triggers oxidative stress, and therefore, antioxidants can be an alternative to muscle recovery. We investigated the effects of antioxidant ascorbic acid (AA) on the morphology, antioxidant enzyme activity, and gene expression in the skeletal muscle of pacu (Piaractus mesopotamicus) following fasting, using in vitro and in vivo strategies. Isolated muscle cells of the pacu were subjected to 72 h of nutrient restriction, followed by 24 h of incubation with nutrients or nutrients and AA (200 µM). Fish were fasted for 15 days, followed by 6 h and 15 and 30 days of refeeding with 100, 200, and 400 mg/kg of AA supplementation. AA addition increased cell diameter and the expression of anabolic and cell proliferation genes in vitro. In vivo, 400 mg/kg of AA increased anabolic and proliferative genes expression at 6 h of refeeding, the fiber diameter and the expression of genes related to cell proliferation at 15 days, and the expression of catabolic and oxidative metabolism genes at 30 days. Catalase activity remained low in the higher supplementation group. In conclusion, AA directly affected the isolated muscle cells, and the higher AA supplementation positively influenced muscle growth after fasting.

Nesfatin-1 and nesfatin-1-like peptide suppress growth hormone synthesis via the AC/PKA/CREB pathway in mammalian somatotrophs

Nesfatin-1 (NESF) and NESF-like peptide (NLP), encoded in nucleobindin 2 and 1 (NUCB2 and NUCB1), respectively, are orphan ligands and metabolic factors. We hypothesized that NESF and NLP suppress growth hormone (GH) synthesis, and aimed to determine whether mammalian somatotrophs are a source and site of action of these peptides. Using immortalized rat somatotrophs (GH3 cells), NUCB expression was determined by qPCR, immunofluorescence and Western blot. NESF and NLP binding to GH3 cells was tested using fluorescence imaging. Both time- and concentration-dependent studies were performed to test whether NESF and NLP affect GH. Moreover, the ability of these peptides to modulate the effects of ghrelin, and cell-signaling pathways were studied. GH3 cells express NUCB mRNAs and protein. Labeled NESF and NLP bind to the surface of GH3 cells, and incubation with either NESF or NLP decreased GH mRNA and protein expression, downregulated pit-1 mRNA, and blocked the GH stimulatory effects of ghrelin. Pre-incubation with either of these peptides reduced CREB phosphorylation by an AC-activator, but not when PKA was directly activated by a cAMP analog. Our results indicate that rat somatotrophs are a source of NUCBs, and that NESF and NLP downregulate GH synthesis through the AC/PKA/CREB signaling pathway.

Dietary valine levels affect growth, protein utilisation, immunity and antioxidant status in juvenile hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

A 6-week growth trial was conducted to evaluate the influences of dietary valine (Val) levels on growth, protein utilisation, immunity, antioxidant status and gut micromorphology of juvenile hybrid groupers. Seven isoenergetic, isoproteic and isolipidic diets were formulated to contain graded Val levels (1·21, 1·32, 1·45, 1·58, 1·69, 1·82 and 1·94 %, DM basis). Each experimental diet was hand-fed to triplicate groups of twelve hybrid grouper juveniles. Results showed that weight gain percentage (WG%), protein productive value, protein efficiency ratio, and feed efficiency were increased as dietary Val level increased, reaching a peak value at 1·58 % dietary Val. The quadratic regression analysis of WG% against dietary Val levels indicated that the optimum dietary Val requirement for hybrid groupers was estimated to be 1·56 %. Gut micromorphology and expression of growth hormone in pituitary, insulin-like growth factor 1, target of rapamycin and S6 kinase 1 in liver were significantly affected by dietary Val levels. In serum, fish fed 1·58 % dietary Val had higher superoxide dismutase, catalase, lysozyme activities and IgM concentrations than fish fed other dietary Val levels. Fish fed 1·58 % dietary Val had higher expression of NF-E2-related factor 2 in head kidney than fish fed other dietary Val levels. Generally, the optimum dietary Val requirement for maximal growth of hybrid groupers was estimated to be 1·56 % of DM, corresponding to 3·16 % of dietary protein, and dietary Val levels affected growth, protein utilisation, immunity and antioxidant status in hybrid groupers.

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.

Rainbow trout slow myoblast cell culture as a model to study slow skeletal muscle, and the characterization of mir-133 and mir-499 families as a case study

Muscle fibres are classified as fast, intermediate and slow. In vitro myoblast cell culture model from fast muscle is a very useful tool to study muscle growth and development; however, similar models for slow muscle do not exist. Owing to the compartmentalization of fish muscle fibres, we have developed a slow myoblast cell culture for rainbow trout (Oncorhynchus mykiss). Slow and fast muscle-derived myoblasts have similar morphology, but with differential expression of slow muscle markers such as slow myhc, sox6 and pgc-1α We also characterized the mir-133 and mir-499 microRNA families in trout slow and fast myoblasts as a case study during myogenesis and in response to electrostimulation. Three mir-133 (a-1a, a-1b and a-2) and four mir-499 (aa, ab, ba and bb) paralogues were identified for rainbow trout and named base on their phylogenetic relationship to zebrafish and Atlantic salmon orthologues. Omy-mir-499ab and omy-mir-499bb had 0.6 and 0.5-fold higher expression in slow myoblasts compared with fast myoblasts, whereas mir-133 duplicates had similar levels in both phenotypes and little variation during development. Slow myoblasts also showed increased expression for omy-mir-499b paralogues in response to chronic electrostimulation (7-fold increase for omy-mir-499ba and 2.5-fold increase for omy-mir-499bb). The higher expression of mir-499 paralogues in slow myoblasts suggests a role in phenotype determination, while the lack of significant differences of mir-133 copies during culture development might indicate a different role in fish compared with mammals. We have also found signs of sub-functionalization of mir-499 paralogues after electrostimulation, with omy-mir-499b copies more responsive to electrical signals.

Regulatory mechanisms involved in muscle and bone remodeling during refeeding in gilthead sea bream

The tolerance of fish to fasting offers a model to study the regulatory mechanisms and changes produced when feeding is restored. Gilthead sea bream juveniles were exposed to a 21-days fasting period followed by 2 h to 7-days refeeding. Fasting provoked a decrease in body weight, somatic indexes, and muscle gene expression of members of the Gh/Igf system, signaling molecules (akt, tor and downstream effectors), proliferation marker pcna, myogenic regulatory factors, myostatin, and proteolytic molecules such as cathepsins or calpains, while most ubiquitin-proteasome system members increased or remained stable. In bone, downregulated expression of Gh/Igf members and osteogenic factors was observed, whereas expression of the osteoclastic marker ctsk was increased. Refeeding recovered the expression of Gh/Igf system, myogenic and osteogenic factors in a sequence similar to that of development. Akt and Tor phosphorylation raised at 2 and 5 h post-refeeding, much faster than its gene expression increased, which occurred at day 7. The expression in bone and muscle of the inhibitor myostatin (mstn2) showed an inverse profile suggesting an inter-organ coordination that needs to be further explored in fish. Overall, this study provides new information on the molecules involved in the musculoskeletal system remodeling during the early stages of refeeding in fish.

Effect of dietary threonine on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂

The experiment was conducted to investigate the effects of dietary threonine (Thr) on growth performance and muscle growth, protein synthesis and antioxidant-related signalling pathways of hybrid catfish Pelteobagrus vachelli♀ × Leiocassis longirostris♂. A total of 1200 fish (14·19 (se 0·13) g) were randomly distributed into six groups with four replicates each, fed six diets with graded level of Thr (9·5, 11·5, 13·5, 15·4, 17·4 and 19·3 g/kg diets) for 56 d. Results showed (P < 0·05) that dietary Thr (1) increased percentage weight gain, specific growth rate, feed efficiency and protein efficiency ratio; (2) up-regulated growth hormone (GH), insulin-like growth factor 1 (IGF-1), proliferating cell nuclear antigen, myogenic regulation factors (MyoD, Myf5, MyoG and Mrf4) and myosin heavy chain (MyHC) mRNA levels; (3) increased muscle protein content via regulating the protein kinase B/target of rapamycin signalling pathway and (4) decreased malondialdehyde and protein carbonyl contents, increased catalase, glutathione-S-transferase, glutathione reductase and GSH activities, up-regulated mRNA levels of antioxidant enzymes related to NFE2-related factor 2 and γ-glutamylcysteine ligase catalytic subunit. These results suggest that Thr has a potential role to improve muscle growth and protein synthesis, which might be due to the regulation of GH-IGF system, muscle growth-related gene, antioxidative capacity and protein synthesis-related signalling pathways. Based on the quadratic regression analysis of specific growth rate, the Thr requirement of hybrid catfish (14·19-25·77 g) was estimated to be 13·77 g/kg of the diet (33·40 g/kg of dietary protein).

Decreased Levels of Serum IGF-1 and Vitamin D Are Associated With Cognitive Impairment in Patients With Type 2 Diabetes

PURPOSE

To determine the association of serum insulin-like growth factor 1 (IGF-1) and vitamin D levels with cognition status in patients with type 2 diabetes mellitus (T2DM).

METHODS

A total of 173 patients with T2DM were recruited and divided into mild cognitive impairment (MCI) group (n = 94) and normal cognition (NC) group (n = 79). Levels of IGF-1 and 25(OH)D were measured and compared, and the correlations among IGF-1, 25(OH)D, and cognitive function were analyzed.

RESULTS

Insulin-like growth factor 1 and 25(OH)D levels significantly decreased in MCI group than those in the NC group (both P < .001). Multiple stepwise regression analysis revealed that IGF-1 (β = .146, P < .001) and 25(OH)D (β = .199, P < .001) independently predicted Montreal Cognitive Assessment (MoCA) scores. Partial least square regression showed that contributions of both 25(OH)D (P < .001) and IGF-1 (P < .001) to MoCA scores were significant, while no cross-effect was observed between them (P = .714).

CONCLUSIONS

Low serum IGF-1 and 25(OH)D levels may separately predict poor cognitive performance in patients with diabetes.

Non-synonymous polymorphisms in candidate gene associated with growth traits in Channel catfish (Ictalurus punctatus, Rafinesque, 1818)

Resequencing of Myostatin, Growth Hormone, Follistatin-A-like, Insulin-like Growth Factor I (IGF-I) and Myogenin (MYOG) genes was completed to discover novel genetic variations and assess non synonymous (ns) polymorphisms (SNPs) effect on growth related traits of channel catfish. Wild and farmed animals were used as a discovering population. Resequencing lead to the identification of 59 new variants in the five analyzed genes; 66% found in introns and 34% in coding regions. From coding regions, 14 variants were synonyms and six were ns variations. A mutation rate of one in 129 bp was estimated. Four ns variations were selected for validation and association analysis. In IGF-I two ns polymorphisms, at IGF-I19 the G wild type allele was fixed in population and for IGF-I63 the C allele had a frequency of 0.972 and for mutate allele G of 0.027. In MYOG two ns SNPs were assessed. MYOG131 presented a frequency of alleles T and A, of 0.754 and 0.246, respectively and MYOG233, with a frequency of G and C of 0.775 and 0.225, respectively. Only MYOG131 (g.529T>A) was significantly associated (P < 0.04) to some growth traits. Results suggest MYOG131 g.529T>A as candidate locus for genetic enhancement of growth traits in channel catfish.

Gene expression analyses in malformed skeletal structures of gilthead sea bream (Sparus aurata)

The incidence of skeletal anomalies in reared fish has been translated for years in important economic losses for the aquaculture industry. In the present study, we have analysed the gene expression of extracellular matrix components and transcription factors involved in bone development in gilthead sea bream presenting different skeletal anomalies: lordosis (LD), lordosis-scoliosis-kyphosis (LSK) or opercular, dental or jaw malformations in comparison with control (CT) specimens. Results showed a possible link between the presence of LD and LSK and the significant downregulation of genes involved in osteoblasts' maturation and matrix mineralization (collagen type 1-alpha, osteopontin, osteocalcin, matrix Gla protein and tissue non-specific alkaline phosphatase), as well as in bone resorption (cathepsin K and matrix metalloproteinase 9) compared to CT animals. Contrarily, the key osteogenic transcription factor runx2 was upregulated in the malformed vertebra suggesting impaired determination of mesenchymal stem cells towards the osteoblastic lineage. Despite the gene expression patterns of the other malformed structures were not affected in comparison with CT fish, the results of the present study may contribute in the long term to identify potential candidate gene profiles associated with column deformities that may help reducing the incidence of appearance of skeletal anomalies in this important aquaculture species.

A long-term growth hormone treatment stimulates growth and lipolysis in gilthead sea bream juveniles

The enhancement of the endocrine growth hormone (GH)/insulin-like growth factor I (IGF-I) system by the treatment with a sustained release formulation of a recombinant bovine GH (rBGH), is a good strategy to investigate growth optimization in aquaculture fish species. To further deepen into the knowledge of rBGH effects in fish and to estimate the growth potential of juveniles of gilthead sea bream, the present work evaluated rBGH injection on growth, GH/IGF-I axis and lipid metabolism modulation, and explored the conservation of GH effects provoked by the in vivo treatment using in vitro models of different tissues. The rBGH treatment increased body weight and specific growth rate (SGR) in juveniles and potentiated hyperplastic muscle growth while reducing circulating triglyceride levels. Moreover, the results demonstrated that the in vivo treatment enhanced also lipolysis in both isolated hepatocytes and adipocytes, as well as in day 4 cultured myocytes. Furthermore, these cultured myocytes extracted from rBGH-injected fish presented higher gene expression of GH/IGF-I axis-related molecules and myogenic regulatory factors, as well as stimulated myogenesis (i.e. increased protein expression of a proliferation and a differentiation marker) compared to Control fish-derived cells. These data, suggested that cells in vitro can retain some of the pathways activated by in vivo treatments in fish, what can be considered an interesting line of applied research. Overall, the results showed that rBGH stimulates somatic growth, including specifically muscle hyperplasia, as well as lipolytic activity in gilthead sea bream juveniles.

Ascorbic acid stimulates the in vitro myoblast proliferation and migration of pacu (Piaractus mesopotamicus)

The postembryonic growth of skeletal muscle in teleost fish involves myoblast proliferation, migration and differentiation, encompassing the main events of embryonic myogenesis. Ascorbic acid plays important cellular and biochemical roles as an antioxidant and contributes to the proper collagen biosynthesis necessary for the structure of connective and bone tissues. However, whether ascorbic acid can directly influence the mechanisms of fish myogenesis and skeletal muscle growth remains unclear. The aim of our work was to evaluate the effects of ascorbic acid supplementation on the in vitro myoblast proliferation and migration of pacu (Piaractus mesopotamicus). To provide insight into the potential antioxidant role of ascorbic acid, we also treated myoblasts in vitro with menadione, which is a powerful oxidant. Our results show that ascorbic acid-supplemented myoblasts exhibit increased proliferation and migration and are protected against the oxidative stress caused by menadione. In addition, ascorbic acid increased the activity of the antioxidant enzyme superoxide dismutase and the expression of myog and mtor, which are molecular markers related to skeletal muscle myogenesis and protein synthesis, respectively. This work reveals a direct influence of ascorbic acid on the mechanisms of pacu myogenesis and highlights the potential use of ascorbic acid for stimulating fish skeletal muscle growth.

Essential amino acids exhibit variable effects on protein degradation in rainbow trout (Oncorhynchus mykiss) primary myocytes

The functional role of amino acids as regulators of protein degradation was investigated using primary myogenic precursor cell culture as in vitro model of rainbow trout white muscle. Seven-day old myocytes were starved of amino acids for two hours then exposed to media that contained amino acid treatments, during which protein degradation rates were analyzed over five hours by measuring cellular release of ³H-tyrosine. Increasing concentrations of essential amino acids (EAA) reduced protein degradation rates; this effect was dose-dependent within the physiological range found in plasma. Addition of leucine or phenylalanine at 5 mM and 2.5 mM, respectively, decreased rates of protein degradation compared to media without amino acid supplementation, suggesting that these amino acids directly regulate muscle proteolysis. Protein degradation rates were similar in cells exposed to media without EAA and media lacking only leucine, further supporting a role for leucine as a central regulator of protein turnover. Addition of 5 mM lysine or valine to media without amino acids increased protein degradation; this response was attenuated as EAA were added back into media, supporting that a lysine or valine imbalance is costly for muscle protein retention. In summary, there is evidence for amino acids as both positive and negative regulators of protein turnover in rainbow trout muscle. These findings suggest that there may be an optimal plasma amino acid profile that minimizes protein turnover and that this could be achieved through diet formulation.

Oceanographic upwelling conditions influence signaling pathways involved in muscle growth of intertidal fish

Few studies have addressed the impact of the upwelling oceanographical conditions on biological processes, such as growth, using a molecular and physiological approach. Upwelling conditions are characterized by low temperature seawater and high nutrient availability, which represents an ideal opportunity to understand how habitat modulates animal performance at different levels of biological complexity. We aimed to assess intraspecific variations in weight, oxygen consumption, protein content, and key signaling pathways involved in muscle-growth (protein kinase B (AKT) and extracellular signal-regulated kinase (ERK)) under experimental trials considering high/low seawater temperatures with full/restricted food rations. For this purpose, we studied Girella laevifrons, one of the most abundant fish species inhabiting rocky intertidal zones along the Eastern South Pacific coasts. Using fish obtained from upwelling (U) and non-upwelling (NU) zones, we reported that U animals displayed higher growth performance during both contrasting trials, with a weight gain (~3 g), lower oxygen consumption (~12%), and higher protein contents (~20%). Only ERK showed significant differences during the trials (~2-fold downregulation between NU and U fish). We also found that U fish increased protein ubiquitination in high water temperature and restricted food ration in contrast to NU fish. Our results help to elucidate how upwelling conditions may influence fish growth at physiological and molecular levels. Still, future analyses are necessary to improve the information regarding the impact of U and NU condition on animals, as well as the possible applications of this data in the aquaculture industry.

Recombinant bovine growth hormone (rBGH) enhances somatic growth by regulating the GH-IGF axis in fingerlings of gilthead sea bream (Sparus aurata)

The growth hormone (GH)/insulin-like growth factors (IGFs) endocrine axis is the main growth-regulator system in vertebrates. Some authors have demonstrated the positive effects on growth of a sustained-release formulation of a recombinant bovine GH (rBGH) in different fish species. The aim of this work was to characterize the effects of a single injection of rBGH in fingerlings of gilthead sea bream on growth, GH-IGF axis, and both myogenic and osteogenic processes. Thus, body weight and specific growth rate were significantly increased in rBGH-treated fish respect to control fish at 6weeks post-injection, whereas the hepatosomatic index was decreased and the condition factor and mesenteric fat index were unchanged, altogether indicating enhanced somatic growth. Moreover, rBGH injection increased the plasma IGF-I levels in parallel with a rise of hepatic mRNA from total IGF-I, IGF-Ic and IGF-II, the binding proteins IGFBP-1a and IGFBP-2b, and also the receptors IGF-IRb, GHR-I and GHR-II. In skeletal muscle, the expression of IGF-Ib and GHR-I was significantly increased but that of IGF-IRb was reduced; the mRNA levels of myogenic regulatory factors, proliferation and differentiation markers (PCNA and MHC, respectively), or that of different molecules of the signaling pathway (TOR/AKT) were unaltered. Besides, the growth inhibitor myostatin (MSTN1 and MSTN2) and the hypertrophic marker (MLC2B) expression resulted significantly enhanced, suggesting altogether that the muscle is in a non-proliferative stage of development. Contrarily in bone, although the expression of most molecules of the GH/IGF axis was decreased, the mRNA levels of several osteogenic genes were increased. The histology analysis showed a GH induced lipolytic effect with a clear decrease in the subcutaneous fat layer. Overall, these results reveal that a better growth potential can be achieved on this species and supports the possibility to improve growth and quality through the optimization of its culture conditions.

The Mitotic and Metabolic Effects of Phosphatidic Acid in the Primary Muscle Cells of Turbot (Scophthalmus maximus)

Searching for nutraceuticals and understanding the underlying mechanism that promote fish growth is at high demand for aquaculture industry. In this study, the modulatory effects of soy phosphatidic acids (PA) on cell proliferation, nutrient sensing, and metabolic pathways were systematically examined in primary muscle cells of turbot (Scophthalmus maximus). PA was found to stimulate cell proliferation and promote G1/S phase transition through activation of target of rapamycin signaling pathway. The expression of myogenic regulatory factors, including myoD and follistatin, was upregulated, while that of myogenin and myostatin was downregulated by PA. Furthermore, PA increased intracellular free amino acid levels and enhanced protein synthesis, lipogenesis, and glycolysis, while suppressed amino acid degradation and lipolysis. PA also was found to increased cellular energy production through stimulated tricarboxylic acid cycle and oxidative phosphorylation. Our results identified PA as a potential nutraceutical that stimulates muscle cell proliferation and anabolism in fish.

Proteolytic systems' expression during myogenesis and transcriptional regulation by amino acids in gilthead sea bream cultured muscle cells

Proteolytic systems exert an important role in vertebrate muscle controlling protein turnover, recycling of amino acids (AA) or its use for energy production, as well as other functions like myogenesis. In fish, proteolytic systems are crucial for the relatively high muscle somatic index they possess, and because protein is the most important dietary component. Thus in this study, the molecular profile of proteolytic markers (calpains, cathepsins and ubiquitin-proteasome system (UbP) members) were analyzed during gilthead sea bream (Sparus aurata) myogenesis in vitro and under different AA treatments. The gene expression of calpains (capn1, capn3 and capns1b) decreased progressively during myogenesis together with the proteasome member n3; whereas capn2, capns1a, capns1b and ubiquitin (ub) remained stable. Contrarily, the cathepsin D (ctsd) paralogs and E3 ubiquitin ligases mafbx and murf1, showed a significant peak in gene expression at day 8 of culture that slightly decreased afterwards. Moreover, the protein expression analyzed for selected molecules presented in general the same profile of the mRNA levels, which was confirmed by correlation analysis. These data suggest that calpains seem to be more important during proliferation, while cathepsins and the UbP system appear to be required for myogenic differentiation. Concerning the transcriptional regulation by AA, the recovery of their levels after a short starvation period did not show effects on cathepsins expression, whereas it down-regulated the expression of capn3, capns1b, mafbx, murf1 and up-regulated n3. With regards to AA deficiencies, the major changes occurred at day 2, when leucine limitation suppressed ctsb and ctsl expression. Besides at the same time, both leucine and lysine deficiencies increased the expression of mafbx and murf1 and decreased that of n3. Overall, the opposite nutritional regulation observed, especially for the UbP members, points out an efficient and complementary role of these factors that could be useful in gilthead sea bream diets optimization.

Nutrient sensing and metabolic changes after methionine deprivation in primary muscle cells of turbot (Scophthalmus maximus L.)

The low methionine content in plant-based diets is a major limiting factor for feed utilization by animals. However, the molecular consequences triggered by methionine deficiency have not been well characterized, especially in fish species, whose metabolism is unique in many aspects and important for aquaculture industry. In the present study, the primary muscle cells of turbot (Scophthalmus maximus L.) were isolated and treated with or without methionine for 12 h in culture. The responses of nutrient sensing pathways, the proteomic profiling of metabolic processes, and the expressions of key metabolic molecules were systematically examined. Methionine deprivation (MD) suppressed target of rapamycin (TOR) signaling, activated AMP-activated protein kinase (AMPK) and amino acid response (AAR) pathways. Reduced cellular protein synthesis and increased protein degradation by MD led to increased intracellular free amino acid levels and degradations. MD also reduced glycolysis and lipogenesis while stimulated lipolysis, thus resulted in decreased intracellular lipid pool. MD significantly enhanced energy expenditure through stimulated tricarboxylic acid (TCA) cycle and oxidative phosphorylation. Collectively, our results identified a comprehensive set of transcriptional, proteomic, and signaling responses generated by MD and provided the molecular insight into the integration of cell homeostasis and metabolic controls in fish species.

Upwelling-derived oceanographic conditions impact growth performance and growth-related gene expression in intertidal fish

Growth is one of the main biological processes in aquatic organisms that is affected by environmental fluctuations such as upwelling (characterized by food-rich waters). In fish, growth is directly related with skeletal muscle increase; which represents the largest tissue of body mass. However, the effects of upwelling on growth, at the physiological and molecular level, are unknown. This study used Girella laevifrons (one of the most abundant intertidal fish in Eastern South Pacific) as a biological model, considering animals from upwelling (U) and non-upwelling (NU) areas. Here, we evaluated the effect of nutritional composition and food availability on growth performance and expression of key growth-related genes (insulin-kike growth factor 1 (igf1) and myosin heavy-chain (myhc)) and atrophy-related genes (muscle ring-finger 1 (murf1), F-box only protein 32 (atrogin-1) and BCL2/adenovirus E1B 19kDa-interacting protein 3 (bnip3)). We reported that, among zones, U fish displayed higher growth performance in response to nutritional composition, specifically between protein- and fiber-rich diets (~1g). We also found in NU fish that atrophy-related genes were upregulated with fiber-rich diet and during fasting (~2-fold at minimum respect U). In conclusion, our results suggest that the growth potential of upwelling fish may be a consequence of differential muscle gene expression. Our data provide a preliminary approach contributing on how upwelling influence fish growth at the physiological and molecular levels. Future studies are required to gain further knowledge about molecular differences between U and NU animals, as well as the possible applications of this knowledge in the aquaculture industry.

Tributyltin and triphenyltin exposure promotes in vitro adipogenic differentiation but alters the adipocyte phenotype in rainbow trout

Numerous environmental pollutants have been identified as potential obesogenic compounds affecting endocrine signaling and lipid homeostasis. Among them, well-known organotins such as tributyltin (TBT) and triphenyltin (TPT), can be found in significant concentrations in aquatic environments. The aim of the present study was to investigate in vitro the effects of TBT and TPT on the development and lipid metabolism of rainbow trout (Onchorynchus mykiss) primary cultured adipocytes. Results showed that TBT and TPT induced lipid accumulation and slightly enhanced peroxisome proliferator-activated receptor gamma (PPARγ) and CCAAT enhancer binding protein alpha (C/EBPα) protein expression when compared to a control, both in the presence or absence of lipid mixture. However, the effects were higher when combined with lipid, and in the absence of it, the organotins did not cause complete mature adipocyte morphology. Regarding gene expression analyses, exposure to TBT and TPT caused an increase in fatty acid synthase (fasn) mRNA levels confirming the pro-adipogenic properties of these compounds. In addition, when added together with lipid, TBT and TPT significantly increased cebpa, tumor necrosis factor alpha (tnfa) and ATP-binding cassette transporter 1 (abca1) mRNA levels suggesting a synergistic effect. Overall, our data highlighted that TBT and TPT activate adipocyte differentiation in rainbow trout supporting an obesogenic role for these compounds, although by themselves they are not able to induce complete adipocyte development and maturation suggesting that these adipocytes might not be properly functional.

Caffeic acid and hydroxytyrosol have anti-obesogenic properties in zebrafish and rainbow trout models

Some natural products, known sources of bioactive compounds with a wide range of properties, may have therapeutic values in human health and diseases, as well as agronomic applications. The effect of three compounds of plant origin with well-known dietary antioxidant properties, astaxanthin (ATX), caffeic acid (CA) and hydroxytyrosol (HT), on zebrafish (Danio rerio) larval adiposity and rainbow trout (Onchorynchus mykiss) adipocytes was assessed. The zebrafish obesogenic test (ZOT) demonstrated the anti-obesogenic activity of CA and HT. These compounds were able to counteract the obesogenic effect produced by the peroxisome proliferator-activated receptor gamma (PPARγ) agonist, rosiglitazone (RGZ). CA and HT suppressed RGZ-increased PPARγ protein expression and lipid accumulation in primary-cultured rainbow trout adipocytes. HT also significantly reduced plasma triacylglycerol concentrations, as well as mRNA levels of the fasn adipogenic gene in the adipose tissue of HT-injected rainbow trout. In conclusion, in vitro and in vivo approaches demonstrated the anti-obesogenic potential of CA and HT on teleost fish models that may be relevant for studying their molecular mode of action. Further studies are required to evaluate the effect of these bioactive components as food supplements for modulating adiposity in farmed fish.

Moderate and sustained exercise modulates muscle proteolytic and myogenic markers in gilthead sea bream (Sparus aurata)

Swimming activity primarily accelerates growth in fish by increasing protein synthesis and energy efficiency. The role of muscle in this process is remarkable and especially important in teleosts, where muscle represents a high percentage of body weight and because many fish species present continuous growth. The aim of this work was to characterize the effects of 5 wk of moderate and sustained swimming in gene and protein expression of myogenic regulatory factors, proliferation markers, and proteolytic molecules in two muscle regions (anterior and caudal) of gilthead sea bream fingerlings. Western blot results showed an increase in the proliferation marker proliferating cell nuclear antigen (PCNA), proteolytic system members calpain 1 and cathepsin D, as well as vascular endothelial growth factor protein expression. Moreover, quantitative real-time PCR data showed that exercise increased the gene expression of proteases (calpains, cathepsins, and members of the ubiquitin-proteasome system in the anterior muscle region) and the gene expression of the proliferation marker PCNA and the myogenic factor MyoD in the caudal area compared with control fish. Overall, these data suggest a differential response of the two muscle regions during swimming adaptation, with tissue remodeling and new vessel formation occurring in the anterior muscle and enhanced cell proliferation and differentiation occurring in the caudal area. In summary, the present study contributes to improving the knowledge of the role of proteolytic molecules and other myogenic factors in the adaptation of muscle to moderate sustained swimming in gilthead sea bream.

Protein Profiles for Muscle Development and Intramuscular Fat Accumulation at Different Post-Hatching Ages in Chickens

Muscle development and growth influences the efficiency of poultry meat production, and is closely related to deposition of intramuscular fat (IMF), which is crucial in meat quality. To clarify the molecular mechanisms underlying muscle development and IMF deposition in chickens, protein expression profiles were examined in the breast muscle of Beijing-You chickens at ages 1, 56, 98 and 140 days, using isobaric tags for relative and absolute quantification (iTRAQ). Two hundred and four of 494 proteins were expressed differentially. The expression profile at day 1 differed greatly from those at day 56, 98 and 140. KEGG pathway analysis of differential protein expression from pair-wise comparisons (day 1 vs. 56; 56 vs. 98; 98 vs. 140), showed that the fatty acid degradation pathway was more active during the stage from day 1 to 56 than at other periods. This was consistent with the change in IMF content, which was highest at day 1 and declined dramatically thereafter. When muscle growth was most rapid (days 56-98), pathways involved in muscle development were dominant, including hypertrophic cardiomyopathy, dilated cardiomyopathy, cardiac muscle contraction, tight junctions and focal adhesion. In contrast with hatchlings, the fatty acid degradation pathway was downregulated from day 98 to 140, which was consistent with the period for IMF deposition following rapid muscle growth. Changes in some key specific proteins, including fast skeletal muscle troponin T isoform, aldehyde dehydrogenase 1A1 and apolipoprotein A1, were verified by Western blotting, and could be potential biomarkers for IMF deposition in chickens. Protein-protein interaction networks showed that ribosome-related functional modules were clustered in all three stages. However, the functional module involved in the metabolic pathway was only clustered in the first stage (day 1 vs. 56). This study improves our understanding of the molecular mechanisms underlying muscle development and IMF deposition in chickens.

Decreased Serum IGF-1/IGFBP-3 Molar Ratio is Associated with Executive Function Behaviors in Type 2 Diabetic Patients with Mild Cognitive Impairment

BACKGROUND

Insulin-like growth factor (IGF)-1, through insulin/IGF-1 signaling pathway, is involved in the pathogenesis of type 2 diabetes mellitus (T2DM) and Alzheimer's disease.

OBJECTIVE

This study aimed to assess the association of serum IGF-1 and IGF binding protein (IGFBP)-3 levels with cognition status and to determine whether IGF-1 rs972936 polymorphism is associated with T2DM with mild cognitive impairment (MCI).

METHODS

A total of 150 T2DM patients, 75 satisfying the MCI diagnostic criteria and 75 exhibiting healthy cognition, were enrolled in this study. The cognitive function of the subjects was extensively assessed. Serum IGF-1 and IGFBP-3 levels were measured through enzyme-linked immunosorbent assay; IGF-1/IGFBP-3 molar ratio was calculated. Single nucleotide polymorphisms of the IGF-1-(rs972936) gene were analyzed.

RESULTS

Serum IGF-1/IGFBP-3 molar ratio in MCI patients was significantly lower than that in the control group (p = 0.003). Significant negative correlations were found between IGF-1/IGFBP-3 molar ratio and Trail Making Test A and B (TMT-A and TMT-B) scores (p = 0.003; p <  0.001, respectively), which indicated executive function. Further multiple step-wise regression analysis revealed that the TMT-A or TMT-B score was significantly associated only with serum IGF-1/IGFBP-3 molar ratio (p = 0.016; p <  0.001, respectively). No significant difference was found in the genotype or allele distribution of IGF-1 rs972936 polymorphism between MCI and control groups.

CONCLUSIONS

A low serum IGF-1/IGFBP-3 molar ratio is associated with the pathogenesis of MCI, particularly executive function in T2DM populations. Further investigation with a large population size should be conducted to confirm this observed association.

IGF-I and IGF-II effects on local IGF system and signaling pathways in gilthead sea bream (Sparus aurata) cultured myocytes

The insulin-like growth factors (IGFs) have a fundamental role in a vast range of functions acting through a tyrosine-kinase receptor (IGF-IR). IGFs in muscle can affect the expression of components of the local IGF system, myogenic regulatory factors (MRFs), proliferating (proliferating cell nuclear antigen, PCNA) or differentiating molecules (myosin heavy chain, MHC) and, lead to the activation of different signaling pathways. The response of all these genes to IGFs incubation at two different times in day 4 cultured myocytes of gilthead sea bream was analyzed. Both IGFs increased the expression of IGF-I and IGFBP-5, but showed different effects on the receptors, with IGF-I suppressing the expression of both isoforms (IGF-IRa and IGF-IRb) and IGF-II up-regulating only IGF-IRb. Moreover, the protein levels of PCNA and target of rapamycin (TOR) increased after IGF-II incubation, although a decline in Myf5 and a rise in MHC gene expression was caused by IGF-I. Taken together, these results provide evidence for the importance of IGFs on controlling muscle development and growth in gilthead sea bream and suggest that each IGF may be preferentially acting through a specific IGF-IR. Moreover, the data support the hypothesis that IGF-II has a more important role during proliferation, whereas IGF-I seems to be relevant for the differentiation phase of myogenesis.

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.

Contribution of in vitro myocytes studies to understanding fish muscle physiology

Research on the regulation of fish muscle physiology and growth was addressed originally by classical in vivo approaches; however, systemic interactions resulted in many questions that could be better considered through in vitro myocyte studies. The first paper published by our group in this field was with Tom Moon on brown trout cardiomyocytes, where the insulin and IGF-I receptors were characterized and the down-regulatory effects of an excess of peptides demonstrated. We followed the research on cultured skeletal muscle cells through the collaboration with INRA focused on the characterization of IGF-I receptors and its signaling pathways through in vitro development. Later on, we showed the important metabolic role of IGFs, although these studies were only the first stage of a prolific area of work that has offered a useful tool to advance in our knowledge of the endocrine and nutritional regulation of fish growth and metabolism. Obviously, the findings obtained in vitro serve the purpose to propose the scenario that will need confirmation in vivo, but this technique has made possible many different, easy, fast and better controlled studies. In this review, we have summarized the main advances that the use of cultured muscle cells has permitted, focusing mainly in the role of IGFs regulating fish metabolism and growth. Although many articles have already appeared using this model system in salmonids, gilthead sea bream or zebrafish, it is reasonable to expect new studies with cultured cells using innovative approaches that will help to understand fish physiology and its regulation.

Effects of sustained exercise on GH-IGFs axis in gilthead sea bream (Sparus aurata)

The endocrine system regulates growth mainly through the growth hormone (GH)/insulin-like growth factors (IGFs) axis and, although exercise promotes growth, little is known about its modulation of these factors. The aim of this work was to characterize the effects of 5 wk of moderate sustained swimming on the GH-IGFs axis in gilthead sea bream fingerlings. Plasma IGF-I/GH ratio and tissue gene expression of total IGF-I and three splice variants, IGF-II, three IGF binding proteins, two GH receptors, two IGF-I receptors, and the downstream molecules were analyzed. Fish under exercise (EX) grew more than control fish (CT), had a higher plasma IGF-I/GH ratio, and showed increased hepatic IGF-I expression (mainly IGF-Ia). Total IGF-I expression levels were similar in the anterior and caudal muscles; however, IGF-Ic expression increased with exercise, suggesting that this splice variant may be the most sensitive to mechanical action. Moreover, IGFBP-5b and IGF-II increased in the anterior and caudal muscles, respectively, supporting enhanced muscle growth. Furthermore, in EX fish, hepatic IGF-IRb was reduced together with both GHRs; GHR-II was also reduced in anterior muscle, while GHR-I showed higher expression in the two muscle regions, indicating tissue-dependent differences and responses to exercise. Exercise also increased gene and protein expression of target of rapamycin (TOR), suggesting enhanced muscle protein synthesis. Altogether, these data demonstrate that moderate sustained activity may be used to increase the plasma IGF-I/GH ratio and to potentiate growth in farmed gilthead sea bream, modulating the gene expression of different members of the GH-IGFs axis (i.e., IGF-Ic, IGF-II, IGFBP-5b, GHR-I, and TOR).

Characterisation and expression analysis of cathepsins and ubiquitin-proteasome genes in gilthead sea bream (Sparus aurata) skeletal muscle

Background

The proteolytic enzymes involved in normal protein turnover in fish muscle are also responsible for post-mortem softening of the flesh and are therefore potential determinants of product quality. The main enzyme systems involved are calpains, cathepsins, and the ubiquitin-proteasome (UbP). In this study on Sparus aurata (Sa), the coding sequences of cathepsins (SaCTSB and SaCTSDb) and UbP family members (SaN3 and SaUb) were cloned from fast skeletal muscle, and their expression patterns were examined during ontogeny and in a fasting/re-feeding experiment.

Results

The amino acid sequences identified shared 66-100% overall identity with their orthologues in other vertebrates, with well conserved characteristic functional domains and catalytic residues. SaCTSDb showed phylogenetic, sequence and tissue distribution differences with respect to its paralogue SaCTSDa, previously identified in the ovary. Expression of gilthead sea bream cathepsins (B, L, Da, Db) and UbP members (N3, Ub, MuRF1 and MAFbx) in fast skeletal muscle was determined at three different life-history stages and in response to fasting and re-feeding in juveniles. Most of the proteolytic genes analysed were significantly up-regulated during fasting, and down-regulated with re-feeding and, between the fingerling (15 g) and juvenile/adult stages (~50/500 g), consistent with a decrease in muscle proteolysis in both later contexts. In contrast, SaCTSDa and SaMuRF1 expression was relatively stable with ontogeny and SaUb had higher expression in fingerlings and adults than juveniles.

Conclusions

The data obtained in the present study suggest that cathepsins and UbP genes in gilthead sea bream are co-ordinately regulated during ontogeny to control muscle growth, and indicate that feeding regimes can modulate their expression, providing a potential dietary method of influencing post-mortem fillet tenderisation, and hence, product quality.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1121-0) contains supplementary material, which is available to authorized users.

The TORC1/P70S6K and TORC1/4EBP1 signaling pathways have a stronger contribution on skeletal muscle growth than MAPK/ERK in an early vertebrate: Differential involvement of the IGF system and atrogenes

Knowledge about the underlying mechanisms, particularly the signaling pathways that account for muscle growth in vivo in early vertebrates is still scarce. Fish (Paralichthys adspersus) were fasted for 3weeks to induce a catabolic period of strong muscle atrophy. Subsequently, fish were refed for 2weeks to induce compensatory muscle hypertrophy. During refeeding, the fish were treated daily with either rapamycin (TORC blocker), PD98059 (MEK blocker), or PBS (V; vehicle), or were untreated (C; control). Rapamycin and PD98059 differentially impaired muscle cellularity in vivo, growth performance, and the expression of growth-related genes, and the inhibition of TORC1 had a greater impact on fish muscle growth than the inhibition of MAPK. Blocking TORC1 inhibited the phosphorylation of P70S6K and 4EBP1, two downstream components activated by TORC1, thus affecting protein contents in muscle. Concomitantly, the gene expression in muscle of igf-1, 2 and igfbp-4, 5 was down-regulated while the expression of atrogin-1, murf-1, and igfbp-2, 3 was up-regulated. Muscle hypertrophy was abolished and muscle atrophy was promoted, which finally affected body weight. TORC2 complex was not affected by rapamycin. On the other hand, the PD98059 treatment triggered ERK inactivation, a downstream component activated by MEK. mRNA contents of igf-1 in muscle were down-regulated, and muscle hypertrophy was partially impaired. The present study provides the first direct data on the in vivo contribution of TORC1/P70S6K, TORC1/4EBP1, and MAPK/ERK signaling pathways in the skeletal muscle of an earlier vertebrate, and highlights the transcendental role of TORC1 in growth from the cellular to organism level.

Skeletal muscle plasticity induced by seasonal acclimatization involves IGF1 signaling: implications in ribosomal biogenesis and protein synthesis

One of the most fundamental biological processes in living organisms that are affected by environmental fluctuations is growth. In fish, skeletal muscle accounts for the largest proportion of body mass, and the growth of this tissue is mainly controlled by the insulin-like growth factor (IGF) system. By using the carp (Cyprinus carpio), a fish that inhabits extreme conditions during winter and summer, we assessed the skeletal muscle plasticity induced by seasonal acclimatization and the relation of IGF signaling with protein synthesis and ribosomal biogenesis. The expression of igf1 in muscle decreased during winter in comparison with summer, whereas the expression for both paralogues of igf2 did not change significantly between seasons. The expression of igf1 receptor a (igf1ra), but not of igf1rb, was down-regulated in muscle during the winter as compared to the summer. A decrease in protein contents and protein phosphorylation for IGF signaling molecules in muscle was observed in winter-acclimatized carp. This was related with a decreased expression in muscle for markers of myogenesis (myoblast determination factor (myod), myogenic factor 5 (myf5), and myogenin (myog)); protein synthesis (myosin heavy chain (mhc) and myosin light chain (mlc3 and mlc1b)); and ribosomal biogenesis (pre-rRNA and ribosomal proteins). IGF signaling, and key markers of ribosomal biogenesis, protein synthesis, and myogenesis were affected by seasonal acclimatization, with differential regulation in gene expression and signaling pathway activation observed in muscle between both seasons. This suggests that these molecules are responsible for the muscle plasticity induced by seasonal acclimatization in carp.