Optimal dietary lipid levels alleviated adverse effects of high temperature on growth, lipid metabolism, antioxidant and immune responses in juvenile turbot (Scophthalmus maximus L.)

Fish physiological health is often negatively impacted by high-temperature environments and there are few studies on how dietary lipids affect fish growth and physiology when exposed to heat stress. The main objective of this research was to examine the impact of dietary lipid levels on growth and physiological status of juvenile turbot (Scophthalmus maximus L.) and determine if dietary lipid concentration could alleviate the possible adverse effects of heat stress. Five diets containing 6.81%, 9.35%, 12.03%, 14.74%, and 17.08% lipid, respectively, were formulated and fed to turbot (initial weight 5.13 ± 0.02 g) under high-temperature conditions (24.0-25.0 °C). Meanwhile, the diet with 12.03% lipid (considered by prior work to be an optimal dietary lipid level) was fed to turbot of the same size at normal temperature. Results suggested that, among the different dietary lipid levels under high-temperature conditions, fish fed the optimal lipid (12.03%) exhibited better growth compared to non-optimal lipid groups, as evidenced by higher weight gain and specific growth rate. Simultaneously, the optimal lipid diet may better maintain lipid homeostasis, as attested by lower liver and serum lipid, along with higher liver mRNA levels of lipolysis-related genes (pgc1α, lipin1, pparα, lpl and hl) and lower levels of synthesis-related genes (lxr, fas, scd1, pparγ, dgat1 and dgat2). Also, the optimal lipid diet might mitigate oxidative damage by improving antioxidant enzyme activity, decreasing malondialdehyde levels, and up-regulating oxidation-related genes (sod1, sod2, cat, gpx and ho-1). Furthermore, the optimal lipid may enhance fish immunity, as suggested by the decrease in serum glutamic-oxalacetic/pyruvic transaminase activities, down-regulation of pro-inflammatory genes and up-regulation of anti-inflammation genes. Correspondingly, the optimal lipid level suppressed MAPK signaling pathway via decreased phosphorylation levels of p38, JNK and ERK proteins in liver. In summary, the optimal dietary lipid level facilitated better growth and physiological status in turbot under thermal stress.

Dietary methanotroph bacteria meal alleviates soybean meal-induced enteritis by improving immune tolerance and intestinal flora profile of juvenile turbot (Scophthalmus maximus L.)

An 8-week growth trial was performed to investigate the protective effects of methanotroph bacteria meal (MBM) produced from methane against soybean meal-induced enteritis (SBMIE) in juvenile turbot (Scophthalmus maximus L.). Five isonitrogenous and isolipidic diets were formulated: fishmeal-based diet (FM, the control group); FM with approximate 50% of fishmeal substituted by 399.4 g/kg soybean meal (SBM); SBM supplemented with 63.6, 127.2 and 190.8 g/kg MBM (named MBM1, MBM2 and MBM3), each diet was randomly assigned to triplicate fibreglass tanks. Results showed that fish fed with SBM exhibited enteritis, identified by reduced relative weight of intestine (RWI), as well as expanded lamina propria width and up-regulated gene expression of pro-inflammatory cytokines (tnf-α, il-6 and il-8) in intestine. While the above symptoms were reversed when diet SBM supplemented with MBM at the levels of 63.6 and 127.2 g/kg, as well as characterized by up-regulated gene expression of anti-inflammatory cytokines (tgf-β and il-10) and tight junction protein (claudin3, claudin4 and claudin7) in intestine. Intestinal transcriptome analysis showed that the differentially expressed genes between groups FM and SBM predominantly enriched in the JAK-STAT signaling pathway, and the enrichment of differentially expressed genes between groups SBM and SBM supplemented with 63.6 g/kg MBM was in the inflammatory bowel disease (IBD) and JAK-STAT signaling pathway. To be specific, the expression of jak1, jak2b, stat1 and stat5a was significantly up-regulated when fish fed with SBM, suggested the activation of JAK-STAT signaling pathway, while the expression of these above genes was depressed by providing MBM to diet SBM, and the gene expression of toll-like receptors tlr2 and tlr5b showed a similar pattern. Moreover, intestinal flora analysis showed that community richness and abundance of beneficial bacteria (Cetobacterium and acillus_coagulans) were improved when fish fed with SBM supplemented with 63.6 g/kg MBM. Overall, methanotroph bacteria meal may alleviate SBMIE by regulating the expression of tight junction protein, toll-like receptors and JAK-STAT signaling pathway, as well as improving intestinal flora profile, which would be beneficial for enhancing the immune tolerance and utilization efficiency of turbot to dietary soybean meal.

Ascorbic acid biosynthesis in Pacific abalone Haliotis discus hannai Ino and L-gulonolactone oxidase gene loss as an independent event

Up to now, it has been believed that invertebrates are unable to synthesize ascorbic acid (AA) in vivo. However, in the present study, the full-length CDs (Coding sequence) of L-gulonolactone oxidase (GLO) from Pacific abalone (Haliotis discus hannai Ino) were obtained through molecular cloning. The Pacific abalone GLO contained a FAD-binding domain in the N-termination, and ALO domain and conserved HWAK motif in the C-termination. The GLO gene possesses 12 exons and 11 introns. The Pacific abalone GLO was expressed in various tissues, including the kidney, digestive gland, gill, intestine, muscle and mantle. The GLO activity assay revealed that GLO activity was only detected in the kidney of Pacific abalone. After a 100-day feeding trial, dietary AA levels did not significantly affect the survival, weight gain, daily increment in shell length, and feed conversion ratio of Pacific abalone. The expression of GLO in the kidney was downregulated by dietary AA. These results implied that the ability to synthesize AA in abalone had not been lost. From the evolutionary perspective, the loss of GLO occurred independently as an independent event by matching with the genomes of various species. The positive selection analysis revealed that the GLO gene underwent purifying selective pressure during its evolution. In conclusion, the present study provided direct evidence to prove that the GLO activity and the ability to synthesize AA exist in abalone. The AA synthesis ability in vertebrates might have originated from invertebrates dating back 930.31 million years.

Differences in diacylglycerol acyltransferases expression patterns and regulation cause distinct hepatic triglyceride deposition in fish

Triglyceride (TAG) deposition in the liver is associated with metabolic disorders. In lower vertebrate, the propensity to accumulate hepatic TAG varies widely among fish species. Diacylglycerol acyltransferases (DGAT1 and DGAT2) are major enzymes for TAG synthesis. Here we show that large yellow croaker (Larimichthys crocea) has significantly higher hepatic TAG level than that in rainbow trout (Oncorhynchus mykiss) fed with same diet. Hepatic expression of DGATs genes in croaker is markedly higher compared with trout under physiological condition. Meanwhile, DGAT1 and DGAT2 in both croaker and trout are required for TAG synthesis and lipid droplet formation in vitro. Furthermore, oleic acid treatment increases DGAT1 expression in croaker hepatocytes rather than in trout and has no significant difference in DGAT2 expression in two fish species. Finally, effects of various transcription factors on croaker and trout DGAT1 promoter are studied. We find that DGAT1 is a target gene of the transcription factor CREBH in croaker rather than in trout. Overall, hepatic expression and transcriptional regulation of DGATs display significant species differences between croaker and trout with distinct hepatic triglyceride deposition, which bring new perspectives on the use of fish models for studying hepatic TAG deposition.

Vitamin D promotes the folate transport and metabolism in zebrafish (Danio rerio)

Vitamin D (VD) is a fat-soluble sterol that possesses a wide range of physiological functions. The present study aimed to evaluate the effects of VD on folate metabolism in zebrafish and further investigated the underlying mechanism. Wild-type (WT) zebrafish were fed with a diet containing 0 IU/kg VD3 or 800 IU/kg VD3 for 3 wk. Meanwhile, cyp2r1 mutant zebrafish with impaired VD metabolism was used as another model of VD deficiency. Our results showed that VD deficiency in zebrafish suppressed the gene expression of folate transporters, including reduced folate carrier (RFC) and proton-coupled folate transporter (PCFT) in the intestine. Moreover, VD influenced the gene expression of several enzymes related to cellular folate metabolism in the intestine and liver of zebrafish. Importantly, VD-deficient zebrafish contained a remarkably lower level of folate content in the liver. Notably, VD was incapable of altering folate metabolism in zebrafish when gut microbiota was depleted by antibiotic treatment. Further studies proved that gut commensals from VD-deficient fish displayed a lower capacity to produce folate than those from WT fish. Our study revealed the potential correlation between VD and folate metabolism in zebrafish, and gut microbiota played a key role in VD-regulated folate metabolism in zebrafish.NEW & NOTEWORTHY Our study has identified that VD influences intestinal uptake and transport of folate in zebrafish while also altering hepatic folate metabolism and storage. Interestingly, the regulatory effects of VD on folate transport and metabolism diminished after the gut flora was interrupted by antibiotic treatment, suggesting that the regulatory effects of VD on folate metabolism in zebrafish are most likely dependent on the intestinal flora.

Sterol Regulatory Element Binding Protein 1: A Mediator for High-Fat Diet-Induced Hepatic Gluconeogenesis and Glucose Intolerance in Fish

BACKGROUND

Sterol regulatory element binding protein (SREBP) 1 is considered to be a crucial regulator for lipid synthesis in vertebrates. However, whether SREBP1 could regulate hepatic gluconeogenesis under high-fat diet (HFD) condition is still unknown, and the underlying mechanism is also unclear.

OBJECTIVES

This study aimed to determine gluconeogenesis-related gene and protein expressions in response to HFD in large yellow croaker and explore the role and mechanism of SREBP1 in regulating the related transcription and signaling.

METHODS

Croakers (mean weight, 15.61 ± 0.10 g) were fed with diets containing 12% crude lipid [control diet (ND)] or 18% crude lipid (HFD) for 10 weeks. The glucose tolerance, insulin tolerance, hepatic gluconeogenesis-related genes, and proteins expressions were determined. To explore the role of SREBP1 in HFD-induced gluconeogenesis, SREBP1 was inhibited by pharmacologic inhibitor (fatostatin) or genetic knockdown in croaker hepatocytes under palmitic acid (PA) condition. To explore the underlying mechanism, luciferase reporter and chromatin immunoprecipitation assays were conducted in HEK293T cells. Data were analyzed using analysis of variance or Student t test.

RESULTS

Compared with ND, HFD increased the mRNA expressions of gluconeogenesis genes (2.40-fold to 2.60-fold) (P < 0.05) and reduced protein kinase B (AKT) phosphorylation levels (0.28-fold to 0.34-fold) (P < 0.05) in croakers. However, inhibition of SREBP1 by fatostatin addition or SREBP1 knockdown reduced the mRNA expressions of gluconeogenesis genes (P < 0.05) and increased AKT phosphorylation levels (P < 0.05) in hepatocytes, compared with that by PA treatment. Moreover, fatostatin addition or SREBP1 knockdown also increased the mRNA expressions of irs1 (P < 0.05) and reduced serine phosphorylation of IRS1 (P < 0.05). Furthermore, SREBP1 inhibited IRS1 transcriptions by binding to its promoter and induced IRS1 serine phosphorylation by activating diacylglycerol-protein kinase Cε signaling.

CONCLUSIONS

This study reveals the role of SREBP1 in hepatic gluconeogenesis under HFD condition in croakers, which may provide a potential strategy for improving HFD-induced glucose intolerance.

Palmitic acid activates NLRP3 inflammasome through NF-κB and AMPK-mitophagy-ROS pathways to induce IL-1β production in large yellow croaker (Larimichthys crocea)

Studies on marine fish showed that vegetable oils substituted for excessive fish oil increased interleukin-1β (IL-1β) production. However, whether the nucleotide-binding oligomerization domain, leucine-rich repeat-containing family, pyrin domain-containing-3 (NLRP3) inflammasome has a substantial role in fatty acid-induced IL-1β production in fish remains unclear. The associated specific mechanism is also unknown. In this study, nlrp3, caspase-1 and apoptosis-associated speck-like protein containing a CARD (asc) were successfully cloned, and NLRP3 inflammasome consisted of NLRP3, caspase-1 and ASC in large yellow croaker. Primary hepatocytes of fish incubated with palmitic acid (PA) exhibited the highest expression of pro-inflammatory genes (il-1β and tnfα) and NLRP3 inflammasome related genes (nlrp3, caspase-1 and asc), caspase-1 activity and IL-1β production among different treatments. Furthermore, PA-induced NLRP3 inflammasome activation was confirmed to require two signals: the first signal was that PA promoted the NF-κB (P65) protein into the nucleus, and NF-κB increased NLRP3 promoter activity and nlrp3 transcription. The second signal was that PA inhibited AMPK phosphorylation and decreased mitophagy by inhibiting the expression of PINK and parkin proteins, thereby damaging the mitochondria that could not be effectively cleared. Mitochondrial damage generated excessive amounts of reactive oxygen species, which activated the NLRP3 inflammasome and then induced caspase-1 activity and IL-1β production. Therefore, excessive dietary PA activated NLRP3 inflammasome through NF-κB and AMPK-mitophagy-ROS pathways to induce IL-1β production, thereby leading to inflammation in fish.

Dietary palm oil enhances Sterol regulatory element-binding protein 2-mediated cholesterol biosynthesis through inducing endoplasmic reticulum stress in muscle of large yellow croaker (Larimichthys crocea)

Sterol regulatory element-binding protein 2 (SREBP2) is considered to be a major regulator to control cholesterol homoeostasis in mammals. However, the role of SREBP2 in teleost remains poorly understand. Here, we explored the molecular characterisation of SREBP2 and identified SREBP2 as a key modulator for 3-hydroxy-3-methylglutaryl-coenzyme A reductase and 7-dehydrocholesterol reductase, which were rate-limiting enzymes of cholesterol biosynthesis. Moreover, dietary palm oil in vivo or palmitic acid (PA) treatment in vitro elevated cholesterol content through triggering SREBP2-mediated cholesterol biosynthesis in large yellow croaker. Furthermore, our results also found that PA-induced activation of SREBP2 was dependent on the stimulating of endoplasmic reticulum stress (ERS) in croaker myocytes and inhibition of ERS by 4-Phenylbutyric acid alleviated PA-induced SREBP2 activation and cholesterol biosynthesis. In summary, our findings reveal a novel insight for understanding the role of SREBP2 in the regulation of cholesterol metabolism in fish and may deepen the link between dietary fatty acid and cholesterol biosynthesis.

Molecular cloning, tissue expression pattern, responses to different fatty acids and potential functions of lysophosphatidylcholine acyltransferase 1 (LPCAT1) in large yellow croaker (Larimichthys crocea)

In farmed fish, diets rich in palm oil have been observed to promote abnormal lipid build-up in the liver, subsequently leading to physiological harm and disease onset. Emerging research suggests that integrating phospholipids into the feed could serve as a potent countermeasure against hepatic impairments induced by vegetable oil consumption. Phosphatidylcholine is the most abundant type among phospholipids. In the metabolic processes of mammal, lysophosphatidylcholine acyltransferase 1 (LPCAT1), crucial for phosphatidylcholine remodeling, demonstrates a marked affinity towards palmitic acid (PA). Nonetheless, aspects concerning the cloning, tissue-specific distribution, and affinity of the LPCAT1 gene to diverse oil sources have yet to be elucidated in the large yellow croaker (Larimichthys crocea). Within the scope of this study, we successfully isolated and cloned the cDNA of the LPCAT1 gene from the large yellow croaker. Subsequent analysis revealed distinct gene expression patterns of LPCAT1 across ten different tissues of the species. The fully sequenced coding DNA sequence (CDS) of LPCAT1 spans 1503 bp and encodes a sequence of 500 amino acids. Comparative sequence alignment indicates that LPCAT1 shares a 69.75 % amino acid similarity with its counterparts in other species. Although LPCAT1 manifests across various tissues of the large yellow croaker, its predominance is markedly evident in the liver and gills. Furthermore, post exposure of the large yellow croaker's hepatocytes to varied fatty acids, PA has a strong response to LPCAT1. Upon the addition of appropriate lysolecithin to palm oil feed, the mRNA expression of LPCAT1 in the liver cells of the large yellow croaker showed significant variations compared to other subtypes. Concurrently, the mRNA expression of pro-inflammatory genes il-1β, il-6, il-8, tnf-α and ifn-γ in the liver tissue of the large yellow croaker decreased. Interestingly, they exhibit the same trend of change. In conclusion, we have cloned the LPCAT1 gene on fish successfully and find the augmented gene response of LPCAT1 in hepatocytes under PA treatment first. The results of this study suggest that LPCAT1 may be associated with liver inflammation in fish and offer new insights into mitigating liver diseases in fish caused by palm oil feed.

Vitamin D regulates glucose metabolism in zebrafish (Danio rerio) by maintaining intestinal homeostasis

Vitamin D (VD) is a steroid hormone that is widely known to play an important role in maintaining mineral homeostasis, and regulating various physiological functions. Our previous results demonstrated that the interruption of VD metabolism caused hyperglycemia in zebrafish. In the present study we further explored the mechanism that VD regulates glucose metabolism by maintaining intestinal homeostasis in zebrafish. Our results showed that the expression of several peptide hormones including gastric inhibitory peptide, peptide YY, and fibroblast growth factor 19 in the intestine decreased, while the expression of sodium glucose cotransporter-1 and gcg was increased in the intestine of the zebrafish fed with the VD3-deficient diet. Consistently, similar results were obtained in cyp2r1-/- zebrafish, in which endogenous VD metabolism is blocked. Furthermore, the results obtained from germ-free zebrafish exhibited that VD-regulated glucose metabolism was partly dependent on the microbiota in zebrafish. Importantly, the transplantation of gut microbiota collected from cyp2r1-/- zebrafish to germ-free zebrafish led to hyperglycemic symptoms in the fish, which were associated with the altered structure and functions of the microbiota in cyp2r1-/- zebrafish. Interestingly, the treatments with acetate or Cetobacterium somerae, a potent acetate producer, lowered the glucose contents whereas augmented insulin expression in zebrafish larvae. Notably, acetate supplementation alleviated hyperglycemia in cyp2r1-/- zebrafish and other diabetic zebrafish. In conclusion, our study has demonstrated that VD modulates the gut microbiota-SCFAs-gastrointestinal hormone axis, contributing to the maintenance of glucose homeostasis.

In vivo DNA methylation editing in zebrafish

The CRISPR/dCas9-based epigenome editing technique has driven much attention. Fused with a catalytic domain from Dnmt or Tet protein, the CRISPR/dCas9-DnmtCD or -TetCD systems possess the targeted DNA methylation editing ability and have established a series of in vitro and in vivo disease models. However, no publication has been reported on zebrafish (Danio rerio), an important animal model in biomedicine. The present study demonstrated that CRISPR/dCas9-Dnmt7 and -Tet2 catalytic domain fusions could site-specifically edit genomic DNA methylation in vivo in zebrafish and may serve as an efficient toolkit for DNA methylation editing in the zebrafish model.

Regulation of low-density lipoprotein on lipid metabolism in macrophages of large yellow croaker (Larimichthys crocea)

Low-density lipoprotein (LDL) is the main carrier of cholesterol transport in plasma, which participates in regulating lipid homeostasis. Studies in mammals have shown that high levels of LDL in plasma absorbed by macrophages trigger the formation of lipid-rich foam cells, leading to the development of atherosclerotic plaques. Although lipid-rich atherosclerosis-like lesions have been discovered in the aorta of several fish species, the physiological function of LDL in fish macrophages remains poorly understood. In the present study, LDL was isolated from the plasma of large yellow croaker (Larimichthys crocea), and mass spectrometry analysis identified two truncated forms of apolipoprotein B100 in the LDL protein profile. Transcriptomic analysis of LDL-stimulated macrophages revealed that differentially expressed genes (DEGs) were enriched in various pathways related to lipid metabolism, as confirmed by the fact that LDL increased total cholesterol and cholesteryl esters content. Meanwhile, the gene and protein expression levels of perilipin2 (PLIN2), a DEG enriched in the PPAR signaling pathway, were upregulated in response to LDL stimulation. Importantly, knocking down plin2 significantly attenuates LDL-induced cholesterol accumulation and promotes cholesterol efflux. Furthermore, the transcription factor PPARγ, which is upregulated in response to LDL stimulation, can enhance the promoter activity of plin2. In conclusion, this study suggests that LDL may upregulate plin2 expression through PPARγ, resulting in cholesterol accumulation in fish macrophages. This study will facilitate the investigation of the function of LDL in regulating lipid homeostasis in macrophages and shed light on the evolutionary origin of LDL metabolism in vertebrates.

Butyrate induces STAT3/HIF-1α/IL-22 signaling via GPCR and HDAC3 inhibition to activate autophagy in head kidney macrophages from turbot (Scophthalmus maximus L.)

As one of short-chain fatty acids, butyrate is an important metabolite of dietary fiber by the fermentation of gut commensals. Our recent study uncovered that butyrate promoted IL-22 production in fish macrophages to augment the host defense. In the current study, we further explored the underlying signaling pathways in butyrate-induced IL-22 production in fish macrophages. Our results showed that butyrate augmented the IL-22 expression in head kidney macrophages (HKMs) of turbot through binding to G-protein receptor 41 (GPR41) and GPR43. Moreover, histone deacetylase 3 (HDAC3) inhibition apparently up-regulated the butyrate-enhanced IL-22 generation, indicating HDACs were engaged in butyrate-regulated IL-22 secretion. In addition, butyrate triggered the STAT3/HIF-1α signaling to elevate the IL-22 expression in HKMs. Importantly, the evidence in vitro and in vivo was provided that butyrate activated autophagy in fish macrophages via IL-22 signaling, which contributing to the elimination of invading bacteria. In conclusion, we clarified in the current study that butyrate induced STAT3/HIF-1α/IL-22 signaling pathway via GPCR binding and HDAC3 inhibition in fish macrophages to activate autophagy that was involved in pathogen clearance in fish macrophages.

Exploring the role of SWI/SNF complex subunit BAF60c in lipid metabolism and inflammation in fish

Chromatin remodeling plays an important role in regulating gene transcription, in which chromatin remodeling complex is a crucial aspect. Brg1/Brm-associated factor 60c (BAF60c) subunit forms a bridge between chromatin remodeling complexes and transcription factors in mammals; hence, it has received extensive attention. However, the roles of BAF60c in fish remain largely unexplored. In this study, we identified BAF60c-interacting proteins by using HIS-pull-down and LC-MS/MS analysis in fish. Subsequently, the RNA-seq analysis was performed to identify the overall effects of BAF60c. Then, the function of BAF60c was verified through BAF60c knockdown and overexpression experiments. We demonstrated for the first time that BAF60c interacts with glucose-regulated protein 78 (GRP78) and regulates lipid metabolism, endoplasmic reticulum (ER) stress, and inflammation. Knockdown of BAF60c reduces fatty acid biosynthesis, ER stress, and inflammation. In conclusion, the results enriched BAF60c-interacting protein network and explored the function of BAF60c in lipid metabolism and inflammation in fish.

Effects of dietary bile acids levels on growth performance, anti-oxidative capacity, immunity and intestinal microbiota of abalone Haliotis discus hannai

Abalone Haliotis discus hannai (initial weight: 38.79 ± 0.70 g) was used as the experimental animal in a 105-day feeding trial to investigate the influence of dietary bile acids levels on the growth, anti-oxidation, immune response and intestinal microbiota. Six isonitrogenous and isolipidic diets were prepared by adding 0 (control group), 15, 30, 60, 120 and 240 mg/kg of bile acids, respectively (named BA0, BA15, BA30, BA60, BA120 and BA240, respectively). It was found that survival of abalone between groups had no significant difference (P > 0.05). Compared to the control, significant improvements in weight gain rate (WGR) were observed in the groups of BA30 and BA60 (P < 0.05). Based on WGR, the broken line regression model analysis showed that the optimum demand for dietary bile acids for abalone was 35.47 mg/kg. Dietary bile acids increased the total anti-oxidative capacity and activities of catalase, superoxide dismutase, lysozyme and alkaline phosphatase, meanwhile decreased the content of malondialdehyde, alanine aminotransferase and aspartate aminotransferase activities in the cell-free hemolymph (P < 0.05). When bile acids were added to the diets, mRNA levels of genes related to pro-inflammatory factors and apoptosis in the digestive gland were down-regulated (P < 0.05). In contrast, the expression of genes related to anti-oxidation was significantly up-regulated (P < 0.05). The Firmicutes, Actinobacteriota and Proteobacteria were the most abundant phyla in intestine. And dietary bile acids significantly decreased the abundance of Actinobacteria and increased the abundance of Firmicutes (P < 0.05). In conclusion, supplementation of dietary bile acids within 120 mg/kg significantly increased the growth of abalone. The 34.62 mg/kg of dietary bile acids significantly increased the anti-oxidative capacity of abalone. Appropriate levels of dietary bile acids (34.62-61.75 mg/kg) promote the immunity of abalone. Application of appropriate levels of bile acids in diets (34.62 mg/kg) changed the intestinal microbiota and promoted the intestinal health of abalone.

Phosphatidylethanolamine alleviates OX-LDL-induced macrophage inflammation by upregulating autophagy and inhibiting NLRP1 inflammasome activation

Oxidized low-density lipoprotein (OX-LDL)-induced inflammation and autophagy dysregulation are important events in the progression of atherosclerosis. Phosphatidylethanolamine (PE), a multifunctional phospholipid that is enriched in cells, has been proven to be directly involved in autophagy which is closely associated with inflammation. However, whether PE can influence OX-LDL-induced autophagy dysregulation and inflammation has not been reported. In the present study, we revealed that OX-LDL significantly induced macrophage inflammation through the CD36-NLRP1-caspase-1 signaling pathway in fish. Meanwhile, cellular PE levels were significantly decreased in response to OX-LDL induction. Based on the relationship between PE and autophagy, we then examined the effect of PE supplementation on OX-LDL-mediated autophagy impairment and inflammation induction in macrophages. As expected, exogenous PE restored impaired autophagy and alleviated inflammation in OX-LDL-stimulated cells. Notably, autophagy inhibitors reversed the inhibitory effect of PE on OX-LDL-induced maturation of IL-1β, indicating that the regulation of PE on OX-LDL-induced inflammation is dependent on autophagy. Furthermore, the positive effect of PE on OX-LDL-induced inflammation was relatively conserved in mouse and fish macrophages. In conclusion, we elucidated the role of the CD36-NLRP1-caspase-1 signaling pathway in OX-LDL-induced inflammation in fish and revealed for the first time that altering PE abundance in OX-LDL-treated cells could alleviate inflammasome-mediated inflammation by inducing autophagy. Given the relationship between OX-LDL-induced inflammation and atherosclerosis, this study prompts that the use of PE-rich foods promises to be a new strategy for atherosclerosis treatment in vertebrates.

Glycerol monolaurate improved intestinal barrier, antioxidant capacity, inflammatory response and microbiota dysbiosis in large yellow croaker (Larimichthys crocea) fed with high soybean oil diets

Glycerol monolaurate (GML) is a potential candidate for regulating metabolic syndrome and inflammatory response. However, the role of GML in modulating intestinal health in fish has not been well determined. In this study, a 70-d feeding trial was conducted to evaluate the effect of GML on intestinal barrier, antioxidant capacity, inflammatory response and microbiota community of large yellow croaker (13.05 ± 0.09 g) fed with high level soybean oil (SO) diets. Two basic diets with fish oil (FO) or SO were formulated. Based on the SO group diet, three different levels of GML 0.02% (SO0.02), 0.04% (SO0.04) and 0.08% (SO0.08) were supplemented respectively. Results showed that intestinal villus height and perimeter ratio were increased in SO0.04 treatment compared with the SO group. The mRNA expressions of intestinal physical barrier-related gene odc and claudin-11 were significantly up-regulated in different addition of GML treatments compared with the SO group. Fish fed SO diet with 0.04% GML addition showed higher activities of acid phosphatase and lysozyme compared with the SO group. The content of malonaldehyde was significantly decreased and activities of catalase and superoxide dismutase were significantly increased in 0.02% and 0.04% GML groups compared with those in the SO group. The mRNA transcriptional levels of inflammatory response-related genes (il-1β, il-6, tnf-α and cox-2) in 0.04% GML treatment were notably lower than those in the SO group. Meanwhile, sequencing analysis of bacterial 16S rRNA V4-V5 region showed that GML addition changed gut microbiota structure and increased alpha diversity of large yellow croaker fed diets with a high level of SO. The correlation analysis results indicated that the change of intestinal microbiota relative abundance strongly correlated with intestinal health indexes. In conclusion, these results demonstrated that 0.02%-0.04% GML addition could improve intestinal morphology, physical barrier, antioxidant capacity, inflammatory response and microbiota dysbiosis of large yellow croaker fed diets with a high percentage of SO.

Comprehensive study on the effect of dietary leucine supplementation on intestinal physiology, TOR signaling and microbiota in juvenile turbot (Scophthalmus maximus L.)

Intestinal damage and inflammation are major health and welfare issues in aquaculture. Considerable efforts have been devoted to enhancing intestinal health, with a specific emphasis on dietary additives. Branch chain amino acids, particularly leucine, have been reported to enhance growth performance in various studies. However, few studies have focused on the effect of leucine on the intestinal function and its underlying molecular mechanism is far from fully illuminated. In the present study, we comprehensively evaluated the effect of dietary leucine supplementation on intestinal physiology, signaling transduction and microbiota in fish. Juvenile turbot (Scophthalmus maximus L.) (10.13 ± 0.01g) were fed with control diet (Con diet) and leucine supplementation diet (Leu diet) for 10 weeks. The findings revealed significant improvements in intestinal morphology and function in the turbot fed with Leu diet. Leucine supplementation also resulted in a significant increase in mRNA expression levels of mucosal barrier genes, indicating enhanced intestinal integrity. The transcriptional levels of pro-inflammatory factors il-1β, tnf-α and irf-1 was decreased in response to leucine supplementation. Conversely, the level of anti-inflammatory factors tgf-β, il-10 and nf-κb were up-regulated by leucine supplementation. Dietary leucine supplementation led to an increase in intestinal complement (C3 and C4) and immunoglobulin M (IgM) levels, along with elevated antioxidant activity. Moreover, dietary leucine supplementation significantly enhanced the postprandial phosphorylation level of the target of rapamycin (TOR) signaling pathway in the intestine. Finally, intestinal bacterial richness and diversity were modified and intestinal bacterial composition was re-shaped by leucine supplementation. Overall, these results provide new insights into the beneficial role of leucine supplementation in promoting intestinal health in turbot, offering potential implications for the use of leucine as a nutritional supplement in aquaculture practices.

Effects of dietary chloroquine on fish growth, hepatic intermediary metabolism, antioxidant and inflammatory responses in turbot

Autophagy is a conserved cellular self-digestion process and is essential for individual growth, cellular metabolism and inflammatory responses. It was responsive to starvation, pathogens infection and environmental stress. However, the information on the regulation of autophagy in fish hepatic intermediary metabolism, antioxidant system, and immune responses were limited. In the present study, turbot with inhibited autophagy flux was built by dietary chloroquine. The hepatic metabolic response, antioxidant enzymes and immune responses were explored. Results showed that dietary chloroquine induced the expression of Beclin 1, SQSTM and LC-3II, and effectively inhibited autophagy flux. Autophagy dysfunction depressed fish growth and feed utilization, while it induced clusters of liver lipid droplets. The genes involved in lipolysis and fatty acid β-oxidation, as well as the lipogenesis-related genes in chloroquine group were depressed. The phosphorylation of AMPK was activated in chloroquine group, and the genes involved in glycolysis were induced. The hepatic content of malonyldialdehyde and the activities of SOD and CAT were induced when autophagy was inhibited. The content of Complement 3, Complement 4 and Immunoglobulin M, as well as the activity of lysozyme in plasma were depressed in chloroquine group. Dietary chloroquine induced the expression of toll-like receptors and stimulated the expression of myd88 and nf-κb p65, as well as the pro-inflammatory cytokines, such as tnf-α and il-1β. The expression of anti-inflammatory cytokine tgf-β was depressed in the chloroquine group. Our results would extend the knowledge on the role of autophagy in teleost and assist in improving fishery production.

Transcriptome-based nutrigenomics analysis reveals the roles of dietary taurine in the muscle growth of juvenile turbot (Scophthalmus maximus)

The present study explored transcriptomics and gene regulation variations in the muscle of turbot fed with dietary taurine. A 70-day feeding trial was conducted using turbot (initial body weight: 3.66 ± 0.02 g) fed with different levels of dietary taurine: 0 % (C), 0.4 % (T2), 1.2 % (T4) and 2.0 % (T6). Two methods were used to analyze and verify the taurine effects on muscle growth: (1) real-time quantitative PCR (qRT-PCR) for the key muscle growth-related genes and (2) transcriptomic analysis by next-generation sequencing (NGS). The results showed that 1.2 % of dietary taurine supplementation significantly increased the expression of muscle growth stimulatory genes, including TauT, myoD, Myf5, myogenin and follistatin. And also, the 1.2 % level significantly decreased the expression of the muscle growth-restricting gene (myostatin). Meanwhile, transcriptomics analysis found that 1.2 % dietary taurine supplementation significantly increased the number of up-regulated genes linked to metabolic pathways. In contrast, taurine significantly enriched the actin cytoskeleton and metabolic pathways in the T4 and T2 groups, respectively. These findings align with the gene ontology (GO) analysis, which indicated a higher number of cellular component (CC) gene expressions at a 1.2 % of dietary taurine compared to a 0.4 % of dietary taurine supplementation. In conclusion, dietary taurine had positive impacts on the growth-stimulatory genes. Moreover, 1.2 % of dietary taurine supplementation is important to the metabolic pathway enrichment.

Discovery, characterization, and adipocyte differentiation regulation in perirenal adipose tissue of large yellow croaker (Larimichthys crocea)

Adipose tissue is an essential tissue for lipid deposition in fish and is associated with excess lipid accumulation in aquaculture. However, the knowledge of the distribution and characterization of adipose tissue in fish still needs further investigation. This study for the first time discovered perirenal adipose tissue (PAT) in large yellow croaker by MRI and CT technologies. Then, the morphological and cytological characteristics of PAT were observed, showing a typical characteristic of white adipose tissue. Meanwhile, the mRNA expression of marker genes of white adipose tissue was highly expressed in PAT compared with the liver and muscle in large yellow croaker. Moreover, based on the discovery of PAT, preadipocytes from PAT were isolated, and the differentiation system of preadipocytes was established. The lipid droplet and TG content of cell were gradually increased during adipocyte differentiation. In addition, mRNA expressions of lipoprotein lipase, adipose triglyceride lipase, and transcription factors related to adipogenesis (cebpα, srebp1, pparα, and pparγ) were quantified to explain the regulation mechanism during the differentiation process. In summary, the present study first discovered perirenal adipose tissue in fish, then explored the characterization of PAT, and revealed the regulation of adipocyte differentiation. These results could advance the understanding of adipose tissue in fish and provide a novel idea for the study of the mechanism of lipid accumulation.

Comparision of nitrogen removal characteristic and microbial community in freshwater and marine recirculating aquaculture systems

Recirculating aquaculture system (RAS) has a good prospect in aquaculture, but its nitrogen removal characteristics and microbial community changes in freshwater and marine water remain unclear. In this study, six RAS were designed and divided into freshwater group and marine water group with salinity of 0‰ and 32‰, respectively, and operated for 54 days to test changes in nitrogen (NH₄⁺-N, NO₂^--N, NO₃^--N), extracellular polymeric substances and microbial communities. The results showed that ammonia nitrogen was rapidly reduced and almost converted to nitrate nitrogen in the freshwater RAS but to nitrite nitrogen in marine RAS. Compared with freshwater RAS, marine RAS had lower tightly bound extracellular polymeric substances and worse stability and settleability condition. 16S rRNA amplicon sequencing reflected significantly lower bacterial diversity and richness in marine RAS. Microbial community structure at phylum level showed lower relative abundance of Proteobacteria, Actinobacteria, Firmicutes, Nitrospirae, but higher abundance of Bacteroidetes under a salinity of 32‰. High salinity decreased the abundance of funtional genera (Nitrosospira, Nitrospira, Pseudomonas, Rhodococcus, Comamonas, Acidovorax, f_Comamonadaceae), which may account for nitrite accumulation and low nitrogen removal capacity in marine RAS. These findings could provide theoretical and practical basis for improving the start-up speed of high-salinity nitrification biofilm.

Vitamin D3/VDR inhibits inflammation through NF-κB pathway accompanied by resisting apoptosis and inducing autophagy in abalone Haliotis discus hannai

Vitamin D3 is believed to be a contributing factor to innate immunity. Vitamin D receptor (VDR) has a positive effect on inhibiting nuclear factor κB (NF-κB)-mediated inflammation. The underlying molecular mechanisms remain unclear, particularly in mollusks. Consequently, this study will investigate the process of vitamin D3/VDR regulating NF-κB pathway and further explore their functions on inflammation, autophagy, and apoptosis in abalone Haliotis discus hannai. Results showed that knockdown of VDR by using siRNA and dsRNA of VDR in vitro and in vivo led to more intense response of NF-κB signaling to lipopolysaccharide and higher level of apoptosis and autophagy. In addition, 1,25(OH)2D3 stimulation after VDR silencing could partially alleviate apoptosis and induce autophagy. Overexpression of VDR restricted the K48-polyubiquitin chain-dependent inhibitor of κB (IκB) ubiquitination and apoptosis-associated speck-like protein containing CARD (ASC) oligomerization. Besides, VDR silencing resulted in increase of ASC speck formation. In further mechanistic studies, we showed that VDR can directly bind to IκB and IKK1 in vitro and in vivo. In the feeding trial, H&E staining, TUNEL, and electron microscope results showed that vitamin D3 deficiency (0 IU/kg) could recruit more basophilic cells and increase more TUNEL-positive apoptotic cells and lipid droplets (LDs) than vitamin D3 supplement (1000 IU/kg and 5000 IU/kg). In summary, abalone VDR plays a negative regulator role in NF-κB-mediated inflammation via interacting with IκB and inhibiting ubiquitin-dependent degradation of IκB. Vitamin D3 in combination with VDR is essential to establish a delicate balance between autophagy and apoptosis in response to inflammation.

Outcome of Immunotherapy in Adrenocortical Carcinoma - A retrospective cohort study

OBJECTIVE

Clinical trials with immune checkpoint inhibitors (ICI) in adrenocortical carcinoma (ACC) have yielded contradictory results. We aimed to evaluate treatment response and safety of ICI in ACC in a real-life setting.

DESIGN

Retrospective cohort study of 54 patients with advanced ACC receiving ICI as compassionate use at six German reference centres between 2016 and 2022.

METHODS

Objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS) and treatment-related adverse events (TRAE) were assessed.

RESULTS

In 52 patients surviving at least 4 weeks after initiation of ICI, ORR was 13.5% (6-26) and DCR 24% (16-41). PFS was 3.0 months (95%CI 2.3-3.7). In all patients, median OS was 10.4 months (3.8-17). 17 TRAE occurred in 15 patients, which was associated with a longer PFS of 5.5 (1.9-9.2) vs. 2.5 (2.0- 3.0) months (HR 0.29, 95%CI 0.13-0.66, p=0.001) and OS of 28.2 (9.5-46.8) vs. 7.0 (4.1-10.2) months (HR 0.34, 95%CI 0.12-0.93). Positive tissue staining for programmed cell death ligand 1 (PD-L1) was associated with a longer PFS of 3.2 (2.6-3.8) vs. 2.3 (1.6-3.0, p<0.05) months. Adjusted for concomitant mitotane use, treatment with nivolumab was associated with lower risk of progression (HR 0.36, 0.15-0.90) and death (HR 0.20, 0.06-0.72) compared to pembrolizumab.

CONCLUSIONS

In the real-life setting we observe a response comparable to other second-line therapies and an acceptable safety profile in ACC patients receiving different ICI. The relevance of PD-L1 as a marker of response and the potentially more favourable outcome in nivolumab treated patients require confirmation.

Short-Term Alternate Feeding between Terrestrially Sourced Oil- and Fish Oil-Based Diets Modulates the Intestinal Microecology of Juvenile Turbot

A nine-week feeding trial was conducted to investigate changes in the intestinal microbiota of turbot in response to alternate feeding between terrestrially sourced oil (TSO)- and fish oil (FO)-based diets. The following three feeding strategies were designed: (1) continuous feeding with the FO-based diet (FO group); (2) weekly alternate feeding between soybean oil (SO)- and FO-based diets (SO/FO group); and (3) weekly alternate feeding between beef tallow (BT)- and FO-based diets (BT/FO group). An intestinal bacterial community analysis showed that alternate feeding reshaped the intestinal microbial composition. Higher species richness and diversity of the intestinal microbiota were observed in the alternate-feeding groups. A PCoA analysis showed that the samples clustered separately according to the feeding strategy, and among the three groups, the SO/FO group clustered relatively closer to the BT/FO group. The alternate feeding significantly decreased the abundance of Mycoplasma and selectively enriched specific microorganisms, including short-chain fatty acid (SCFA)-producing bacteria, digestive bacteria (Corynebacterium and Sphingomonas), and several potential pathogens (Desulfovibrio and Mycobacterium). Alternate feeding may maintain the intestinal microbiota balance by improving the connectivity of the ecological network and increasing the competitive interactions within the ecological network. The alternate feeding significantly upregulated the KEGG pathways of fatty acid and lipid metabolism, glycan biosynthesis, and amino acid metabolism in the intestinal microbiota. Meanwhile, the upregulation of the KEGG pathway of lipopolysaccharide biosynthesis indicates a potential risk for intestinal health. In conclusion, short-term alternate feeding between dietary lipid sources reshapes the intestinal microecology of the juvenile turbot, possibly resulting in both positive and negative effects.

Effects of supplemental octanoate on hepatic lipid metabolism, serum biochemical indexes, antioxidant capacity and inflammation-related genes expression of large yellow croaker (Larimichthys crocea) fed with high soybean oil diet

Dietary high soybean oil (SO) levels might cause hepatic lipid deposition, induce oxidative stress and inflammatory response in aquatic animals, while octanoate (OCT) is beneficial to metabolism and health in mammals. However, the effect of OCT has been studied rarely in aquatic animals. In this study, a 10-week feeding trial was conducted to investigate the effect of supplemental OCT on hepatic lipid metabolism, serum biochemical indexes, antioxidant capacity and inflammatory response of large yellow croaker (Larimichthys crocea) fed with high SO levels diet. The negative control diet contained 7% fish oil (FO), while the positive control diet contained 7% SO. The other four experimental diets were supplemented with 0.7, 2.1, 6.3 and 18.9 g/kg sodium octanoate (OCT) based on the positive control diet. Results showed that OCT supplementation effectively reduced the hepatic crude lipid, triglyceride (TG), total cholesterol (TC) and non-esterified free fatty acids contents, and alleviated lipid accumulation caused by the SO diet. Meanwhile, OCT supplementation decreased the serum TG, TC, alanine transaminase, aspartate transaminase and low-density lipoprotein cholesterol levels, increased the serum high-density lipoprotein cholesterol level, improved the serum lipid profiles and alleviated hepatic injury. Furthermore, with the supplementation of OCT, the mRNA expression of genes related to lipogenesis (acc1, scd1, fas, srebp1, dgat1 and cebpα) and fatty acid (FA) transport (fabp3, fatp and cd36) were down-regulated, while the mRNA expression of genes related to lipolysis (atgl, hsl and lpl) and FA β-oxidation (cpt1 and mcad) were up-regulated. Besides that, dietary OCT increased the total antioxidant capacity, activities of peroxidase, catalase and superoxide dismutase and the content of reduced glutathione, decreased the content of 8-hydroxy-deoxyguanosine and malondialdehyde and relieved hepatic oxidative stress. Supplementation of 0.7 and 2.1 g/kg OCT down-regulated the mRNA expression of genes related to pro-inflammatory cytokines (tnfα, il1β and ifnγ), and suppressed hepatic inflammatory response. In conclusion, supplementation with 0.7-2.1 g/kg OCT could reduce hepatic lipid accumulation, relieve oxidative stress and regulate inflammatory response in large yellow croaker fed the diet with high SO levels, providing a new way to alleviate the hepatic fat deposition in aquatic animals.

Effects of supplemental fulvic acid on survival, growth performance, digestive ability and immunity of large yellow croaker (Larimichthys crocea) larvae

A 30-day feeding trial was designed to evaluate the effect of supplemental fulvic acid (FA) on survival, growth performance, digestive ability and immunity of large yellow croaker (Larimichthys crocea) larvae (initial body weight 11.33 ± 0.57 mg). Four isonitrogenous and isolipids diets containing 0.00%, 0.01%, 0.02% and 0.04% FA were formulated, respectively. Results showed that the supplementation of 0.04% FA significantly improved survival rate of large yellow croaker larvae. Meanwhile, supplemental FA significantly increased final body weight and specific growth rate. Based on the specific growth rate, the optimal supplementation was 0.0135% FA. Larvae fed the diet with 0.01% FA had significantly higher villus height than the control. The supplementation of 0.01%–0.02% FA significantly increased the muscular thickness of intestine. Moreover, supplementation of FA significantly increased mRNA expression of intestinal epithelial proliferation and barrier genes (pcna, zo-1 and zo-2). Diets supplemented with 0.02%–0.04% FA significantly increased the activity of trypsin in the intestinal segment, while 0.01%–0.02% FA significantly increased the activity of trypsin in the pancreatic segment. Compared with the control, supplementation of FA remarkably increased activities of alkaline phosphatase and leucine aminopeptidase in the brush border membrane of intestine. Larvae fed the diet with 0.01% FA significantly increased activities of lysozyme and total nitric oxide synthase. Furthermore, the supplementation of 0.01% to 0.02% FA significantly decreased the mRNA expression of pro-inflammatory cytokines (tnf-α and il-6). Concurrently, supplemental FA significantly increased anti-inflammatory cytokine (il-10) mRNA expression level. In conclusion, this study indicated that the supplementation of FA could improve the survival rate and growth performance of larvae by promoting intestinal development, digestive enzymes activities and innate immunity.

Effects of GRP78 on Endoplasmic Reticulum Stress and Inflammatory Response in Macrophages of Large Yellow Croaker (Larimichthys crocea)

Endoplasmic reticulum (ER) homeostasis plays a vital role in cell physiological functions. Various factors can destroy the homeostasis of the ER and cause ER stress. Moreover, ER stress is often related to inflammation. Glucose-regulated protein 78 (GRP78) is an ER chaperone, which plays a vital role in maintaining cellular homeostasis. Nevertheless, the potential effects of GRP78 on ER stress and inflammation is still not fully elucidated in fish. In the present study, ER stress and inflammation was induced by tunicamycin (TM) or palmitic acid (PA) in the macrophages of large yellow croakers. GRP78 was treated with an agonist/inhibitor before or after the TM/PA treatment. The results showed that the TM/PA treatment could significantly induce ER stress and an inflammatory response in the macrophages of large yellow croakers whereas the incubation of the GRP78 agonist could reduce TM/PA-induced ER stress and an inflammatory response. Moreover, the incubation of the GRP78 inhibitor could further induce TM/PA-induced ER stress and an inflammatory response. These results provide an innovative idea to explain the relationship between GRP78 and TM/PA-induced ER stress or inflammation in large yellow croakers.

Nutrient sensing signaling and metabolic responses in shrimp Litopenaeus vannamei under acute ammonia stress

Ammonia is the primary environmental factor affecting the growth and health of crustaceans. It would induce oxidative stress and metabolic disorders. Extra amount of energy was demanded to maintain the physiological functions under ammonia stress. However, limited information was available on its effects on the main nutrient metabolism, as well as the nutrient sensing signaling pathways. In the present study, shrimp Litopenaeus vannamei were exposed to acute ammonia stress and injected with amino acid solution. The results showed that acute ammonia exposure resulted in lower free amino acid levels in hemolymph, incomplete activation of the mechanistic target of rapamycin (mTOR) signaling and cascaded less protein synthesis in muscle. It induced autophagy and activated the AMP-activated protein kinase (AMPK) pathway. Meanwhile, ammonia exposure enhanced glycolysis and lipogenesis, but inhibited lipolysis. The results characterized the integrated metabolic responses and nutrient signaling to ammonia stress. It provides critical clues to understand the growth performance and physiological responses in shrimp under ammonia stress.

Comparative analysis of nutritional and transcriptional regulation of hacd1 in large yellow croaker (Larimichthys crocea) and rainbow trout (Oncorhynchus mykiss)

3-hydroxyacyl-CoA dehydratases 1 (Hacd1) is a critical enzyme in long-chain polyunsaturated fatty acids (LC-PUFA) biosynthesis. The difference in expression of hacd1 might account for the stronger capacity of LC-PUFA biosynthesis in freshwater fish than in marine fish, but little is known about fish hacd1. Therefore, this study compared the responses of large yellow croaker and rainbow trout hacd1 to different oil sources or fatty acids, and also examined transcriptional regulation of this gene. In this study, hacd1 was highly expressed in the liver of large yellow croaker and rainbow trout, which is the main organ for LC-PUFA biosynthesis. Therefore, we cloned the hacd1 coding sequence, with a phylogenetic analysis showing that this gene is evolutionarily conserved. Its localization to the endoplasmic reticulum (ER), likely also indicates a conserved structure and function. The expression of hacd1 in the liver was significantly decreased after the substitution of soybean oil (SO) for fish oil but was not significantly affected after palm oil (PO) substitution. Linoleic acid (LA) incubation significantly promoted hacd1 expression in primary hepatocytes of large yellow croaker and eicosapentaenoic acid (EPA) incubation significantly promoted hacd1 expression in primary hepatocytes of rainbow trout. Transcription factors STAT4, C/EBPα, C/EBPβ, HNF1, HSF3 and FOXP3 were identified in both large yellow croaker and rainbow trout. HNF1 had a stronger activation effect in rainbow trout than in large yellow croaker. FOXP3 inhibited hacd1 promoter activity in large yellow croaker but had no effect in rainbow trout. Therefore, the differences between HNF1 and FOXP3 affected the expression of hacd1 in the liver thus being responsible for the high capacity of LC-PUFA biosynthesis in rainbow trout.

Transcription factor EB (TFEB) participates in antiviral immune responses independent of mTORC1 in macrophage of large yellow croaker (Larimichthys crocea)

Transcription factor EB (TFEB) plays an integral role in the production of proinflammatory cytokines and chemokines in response to pathogen stimulation in mammals. However, the role of TFEB in antiviral immune responses and the potential regulatory mechanisms in fish remain poorly understood. Here, we cloned and characterized Larimichthys crocea TFEB (LcTFEB) with 524 amino acids and a typical basic helix-loop-helix-leucine zipper domain. LcTFEB could translocate into the nucleus upon starvation and had a comparatively high expression in immune tissues. Similar to the expression of antiviral immune genes, the transcriptional expression and activity of LcTFEB showed a trend of increasing and then decreasing with the prolongation of stimulation. Inhibition of LcTFEB using siRNA dramatically increased the polyinosinic-polycytidylic acid (poly (I:C))-induced interferon response and pro-inflammatory cytokines mRNA expression levels, whereas pharmacological activation and overexpression of LcTFEB exhibited the reverse effects. Mechanically, LcTFEB might promote the expression of IFNh as negative feedback to limit the virus-induced inflammatory responses. Notably, although inhibition of mTORC1 exacerbated poly (I:C)-triggered inflammatory responses, the effects of LcTFEB were independent of mTORC1. Overall, this study revealed an unidentified critical role of LcTFEB in the regulation of antiviral immune responses and promoted the understanding of TFEB in the antiviral immunity of fish macrophages.

Effects of Tributyrin Supplementation on Growth Performance, Intestinal Digestive Enzyme Activity, Antioxidant Capacity, and Inflammation-Related Gene Expression of Large Yellow Croaker (Larimichthys crocea) Fed with a High Level of Clostridium autoethanogenum Protein

An 8-week growth experiment was conducted to investigate effects of tributyrin (TB) supplementation on growth performance, intestinal digestive enzyme activity, antioxidant capacity, and inflammation-related gene expression of juvenile large yellow croaker (Larimichthys crocea) (initial weight of 12.90 ± 0.02 g) fed diets with high level of Clostridium autoethanogenum protein (CAP). In the negative control diet, 40% fish meal was used as the major source of protein (named as FM), while 45% fish meal protein of FM was substituted with CAP (named as FC) to form a positive control diet. Based on the FC diet, grade levels of 0.05%, 0.1%, 0.2%, 0.4%, and 0.8% tributyrin were added to formulate other five experimental diets. Results showed that fish fed diets with high levels of CAP significantly decreased the weight gain rate (WGR) and specific growth rate (SGR) compared with fish fed the FM diet (P < 0.05). WGR and SGR were significantly higher than in fish fed diets with 0.05% and 0.1% tributyrin that fed the FC diet (P < 0.05). Supplementation of 0.1% tributyrin significantly elevated fish intestinal lipase and protease activities compared to FM and FC diets (P < 0.05). Meanwhile, compared to fish fed the FC diet, fish fed diets with 0.05% and 0.1% tributyrin showed remarkably higher intestinal total antioxidant capacity (T-AOC). Malondialdehyde (MDA) content in the intestine of fish fed diets with 0.05%-0.4% tributyrin was remarkably lower than those in the fish fed the FC diet (P < 0.05). The mRNA expressions of tumor necrosis factor α (tnfα), interleukin-1β (il-1β), interleukin-6 (il-6), and interferon γ (ifnγ) were significantly downregulated in fish fed diets with 0.05%-0.2% tributyrin, and the mRNA expression of il-10 was significantly upregulated in fish fed the 0.2% tributyrin diet (P < 0.05). In regard to antioxidant genes, as the supplementation of tributyrin increased from 0.05% to 0.8%, the mRNA expression of nuclear factor erythroid 2-related factor 2 (nrf2) demonstrated a trend of first rising and then decreasing. However, the mRNA expression of Kelch-like ECH-associated protein 1 (keap1) was remarkably lower in fish fed the FC diet than that fed diets with tributyrin supplementation (P < 0.05). Overall, fish fed tributyrin supplementation diets can ameliorate the negative effects induced by high proportion of CAP in diets, with an appropriate supplementation of 0.1%.

Butyrate-induced IL-22 expression in fish macrophages contributes to bacterial clearance

IL-22 has been characterized as a critical cytokine in maintaining barrier integrity and host immunity. So far, it has been known that IL-22 is mainly produced by lymphoid lineage cells. In the present study, we have thoroughly investigated butyrate-induced production and function of IL-22 in fish macrophages. Our results demonstrated that short-chain fatty acids (SCFAs), major microbiota-derived metabolites, promoted the expression of IL-22 in head kidney macrophages (HKMs) of turbot (Scophthalmus maximus L.). Interestingly, butyrate-mediated intracellular bacterial killing in HKMs diminished when IL-22 expression was interfered. Furthermore, the turbot fed the diet containing sodium butyrate (NaB) exhibited significantly lower mortality after bacterial infection, compared to the fish fed a basal diet. At the meantime, a higher level of IL-22 expression and bactericidal activity was detected in HKMs from the turbot fed NaB-supplemented diet. In addition, NaB treatment promoted the expression of antimicrobial peptides (AMPs) β-defensins in zebrafish (Danio rerio). However, butyrate-induced expression of AMPs was reduced in IL-22 mutant zebrafish compared to wild-type (WT) fish. Meanwhile, NaB treatment was incapable to protect IL-22 mutant fish from bacterial infection as it did in WT zebrafish. Importantly, our results demonstrated that IL-22 expression was remarkably suppressed in macrophage-depleted zebrafish, indicating that macrophage might be a cell source of IL-22 production in vivo. In conclusion, all these findings collectively revealed that SCFAs regulated the production and function of IL-22 in fish macrophages, which facilitated host resistance to bacterial invasion.

Dietary l-carnitine regulates liver lipid metabolism via simultaneously activating fatty acid β-oxidation and suppressing endoplasmic reticulum stress in large yellow croaker fed with high-fat diets

Dietary l-carnitine (LC) is a nutritional factor that reduces liver lipid content. However, whether dietary LC can improve lipid metabolism via simultaneous activation of mitochondrial fatty acid (FA) β-oxidation and suppression of endoplasmic reticulum (ER) stress is still unknown. Large yellow croaker were fed with a high-fat diet (HFD) supplemented with dietary LC at 0, 1·2 or 2·4 ‰ for 10 weeks. The results indicated that a HFD supplemented with LC reduced the liver total lipid and TAG content and improved serum lipid profiles. LC supplementation administered to this fish increased the liver antioxidant capacity by decreasing serum and liver malondialdehyde levels and enhancing the liver antioxidant capacity, which then relieved the liver damage. Dietary LC increased the ATP dynamic process and mitochondrial number, decreased mitochondrial DNA damage and enhanced the protein expression of mitochondrial β-oxidation, biogenesis and mitophagy. Furthermore, dietary LC supplementation increased the expression of genes and proteins related to peroxisomal β-oxidation and biogenesis. Interestingly, feeding fish with LC-enriched diets decreased the protein levels indicative of ER stress, such as glucose-regulated protein 78, p-eukaryotic translational initiation factor 2a and activating transcription factor 6. Dietary LC supplementation downregulated mRNA expression relative to FA synthesis, reduced liver lipid and relieved liver damage through regulating β-oxidation and biogenesis of mitochondria and peroxisomes, as well as the ER stress pathway in fish fed with HFD. The present study provides the first evidence that dietary LC can improve lipid metabolism via simultaneously promoting FA β-oxidation capability and suppressing the ER stress pathway in fish.

Long noncoding RNA lincsc5d regulates hepatic cholesterol synthesis by modulating sterol C5 desaturase in large yellow croaker

Although long noncoding RNA (lncRNA) plays a vital role in cholesterol metabolism, very little information is available in fish. Thus, a 10-week feeding experiment was performed to estimate the effects of lncRNA on cholesterol metabolism in large yellow croaker fed with fish oil (FO), soybean oil (SO), olive oil (OO), and palm oil (PO) diets. Results showed that fish fed with OO and PO diets had higher liver total cholesterol (TC) and cholesterol ester (CE) contents compared with fish fed with FO diets. Analysis of the KEGG pathway showed that the steroid biosynthesis pathway was enriched in comparisons FO vs SO, FO vs OO, and FO vs PO. Meanwhile, sterol C5 desaturase (SC5D), a cholesterol synthase, was up-regulated in the steroid biosynthesis pathway. SC5D was widely expressed in all tissues examined, and the highest expression of SC5D was detected in brain. More importantly, a novel lncRNA associated with sc5d gene was identified by RNA sequencing and named as lincsc5d. The tissue distribution of lincsc5d was similar to that of sc5d. A nuclear/cytoplasmic RNA separation assay showed that lincsc5d was a nucleus-enriched lncRNA. qRT-PCR results demonstrated that lincsc5d was markedly up-regulated in the SO, OO, and PO groups. Furthermore, the results of TC content and the lincsc5d and sc5d expression in hepatocytes agreed with in vivo results. In conclusion, this study indicated that vegetable oils, especially OO and PO, increased hepatic cholesterol levels by promoting cholesterol synthesis, and lncRNA lincsc5d and sc5d might be involved in cholesterol synthesis.

Vitamin D influences gut microbiota and acetate production in zebrafish (Danio rerio) to promote intestinal immunity against invading pathogens

Although evidence has shown that vitamin D (VD) influences gut homeostasis, limited knowledge is available how VD regulates intestinal immunity against bacterial infection. In the present study, cyp2r1 mutant zebrafish, lacking the capacity to metabolize VD, and zebrafish fed a diet devoid of VD, were utilized as VD-deficient animal models. Our results confirmed that the expression of antimicrobial peptides (AMPs) and IL-22 was restrained and the susceptibility to bacterial infection was increased in VD-deficient zebrafish. Furthermore, VD induced AMP expression in zebrafish intestine by activating IL-22 signaling, which was dependent on the microbiota. Further analysis uncovered that the abundance of the acetate-producer Cetobacterium in VD-deficient zebrafish was reduced compared to WT fish. Unexpectedly, VD promoted the growth and acetate production of Cetobacterium somerae under culture in vitro. Importantly, acetate treatment rescued the suppressed expression of β-defensins in VD-deficient zebrafish. Finally, neutrophils contributed to VD-induced AMP expression in zebrafish. In conclusion, our study elucidated that VD modulated gut microbiota composition and production of short-chain fatty acids (SCFAs) in zebrafish intestine, leading to enhanced immunity.

Vitamin D3 enhances the antibacterial ability in head-kidney macrophages of turbot (Scophthalmus maximus L.) through C-type lectin receptors

It has been known that vitamin D₃ (VD₃) not only plays an important role in regulating calcium and phosphorus metabolism in animals, but also has extensive effects on immune functions. In this study, the mechanism how VD₃ influences bactericidal ability in turbot was explored. The transcriptomic analysis identified that dietary VD₃ significantly upregulated the gene expression of C-type lectin receptors (CLRs), including mannose receptors (mrc1, mrc2, pla2r1) and collectins (collectin 11 and collectin 12) in turbot intestine. Further results obtained from in vitro experiments confirmed that the gene expression of mannose receptors and collectins in head-kidney macrophages (HKMs) of turbot was induced after the cells were incubated with different concentrations of VD₃ (0, 1, 10 nM) or 1,25(OH)₂D₃ (0, 10, 100 pM). Meanwhile, both phagocytosis and bactericidal functions of HKMs were significantly improved in VD₃ or 1,25(OH)₂D₃-incubated HKMs. Furthermore, phagocytosis and bacterial killing of HKMs decreased after collectin 11 was knocked down. Moreover, VD₃-enhanced antibacterial activities diminished in collectin 11-interfered cells. Interestingly, the evidence was provided in the present study that inactive VD₃ could be metabolized into active 1,25(OH)₂D₃ via hydroxylases encoded by cyp27a1 and cyp27b1 in fish macrophages. In conclusion, VD₃ could be metabolized to 1,25(OH)₂D₃ in HKMs, which promoted the expression of CLRs in macrophages, leading to enhanced bacterial clearance.

Fishmeal Protein Replacement by Defatted and Full-Fat Black Soldier Fly Larvae Meal in Juvenile Turbot Diet: Effects on the Growth Performance and Intestinal Microbiota

A 12-week feeding trial was conducted to investigate the effect of the same fishmeal protein level replaced by black soldier fly larvae (Hermetia illucens) meal (BSFL) with different lipid contents on the growth performance and intestinal health of juvenile turbot (Scophthalmus maximus L.) (initial body weight 12.64 g). Three isonitrogenous and isolipidic diets were formulated: fish meal-based diet (FM), diets DF and FF, in which 14% fish meal protein of the FM diet was replaced by defatted and full-fat BSFL, respectively. There were no significant differences in growth performance, intestinal morphology, and mucosal barrier function between the DF and the FM group. However, diet FF markedly reduced the growth performance, intestinal perimeter ratio, and the gene expression of anti-inflammatory cytokine TGF-β (P < 0.05). Compared to group FF, the communities of intestinal microbiota in group DF were more similar to group FM. Moreover, diet DF decreased the abundance of some potential pathogenic bacteria and enriched the potential probiotics, such as Bacillus. Diet FF obviously altered the composition of intestinal microbiota and increased the abundance of some potential pathogenic bacteria. These results suggested that the application of defatted BSFL showed more positive effects on fish growth and intestinal health than the full-fat BSFL, and the intestinal microbiota was closely involved in these effects.

Organic copper promoted copper accumulation and transport, enhanced low temperature tolerance and physiological health of white shrimp (Litopenaeus vannamei Boone, 1931)

This study was conducted to assess the effects of dietary copper source and level on hematological parameters, copper accumulation and transport, resistance to low temperature, antioxidant capacity and immune response of white shrimp (Litopenaeus vannamei Boone, 1931). Seven experimental diets with different copper sources and levels were formulated: C, no copper supplementation; S, 30 mg/kg copper in the form of CuSO₄·5H₂O; SO, 15 mg/kg copper in CuSO₄·5H₂O + 7.5 mg/kg copper in Cu-proteinate; O1, O2, O3 and O4, 10, 20, 30 and 40 mg/kg copper in the form of Cu-proteinate, respectively. A total of 840 shrimp (5.30 ± 0.04 g) were randomly distributed to 21 tanks (3 tanks/diet, 40 shrimp/tank). An 8-week feeding trial was conducted. The results showed that there was no significant difference in growth performance and whole shrimp chemical compositions among all groups. Compared with inorganic copper, dietary organic copper (O2 and O3) increased total protein, albumin, and glucose content of plasma, while decreased triglyceride and total cholesterol of plasma. Copper concentration in plasma and muscle and gene expression of metallothionein and copper-transporting ATPase 2 like in hepatopancreas were higher in shrimp fed organic copper (SO, O2, O3 and O4). The lowest mortality after low temperature (10 °C) challenge test was observed in the O2 and O3 groups. Organic copper (SO, O2, O3 and O4) significantly enhanced the antioxidant capacity (in terms of higher activities of total superoxide dismutase, copper zinc superoxide dismutase, catalase, glutathione peroxidase and total antioxidant capacity, lower malondialdehyde concentration of plasma, and up-regulated gene expression of superoxide dismutase, copper zinc superoxide dismutase, catalase and glutathione peroxidase of hepatopancreas). Organic copper (SO, O2, O3 and O4) enhanced the immune response (in terms of higher number of total hemocytes, higher activities of acid phosphatase, alkaline phosphatase, phenoloxidase, hemocyanin and lysozyme in plasma, and higher gene expressions of alkaline phosphatase, lysozyme and hemocyanin in hepatopancreas). Inorganic copper (Diet S) also had positive effects on white shrimp compared with the C diet, but the SO, O2, O3 and O4 diets resulted in better results, among which the O2 diet appeared to be the best one. In conclusion, organic copper was more beneficial to shrimp health than copper sulfate.

Effects of Glycyrrhizin (GL) Supplementation on Survival, Growth Performance, Expression of Feeding-Related Genes, Activities of Digestive Enzymes, Antioxidant Capacity, and Expression of Inflammatory Factors in Large Yellow Croaker (Larimichthys crocea) Larvae

A 30-day feeding trial was conducted to determine the effects of dietary glycyrrhizin (GL) on survival, growth performance, expression of feeding-related genes, activities of digestive enzymes, antioxidant capacity, and expression of inflammatory factors of large yellow croaker larvae with an initial weight of 3.78 ± 0.27 mg. Four 53.80% crude protein and 16.40% crude lipid diets were formulated with supplementation of 0%, 0.005%, 0.01%, and 0.02% GL, respectively. Results indicated that larvae fed diets with GL had higher survival rate and specific growth rate than the control (P < 0.05). Compared with the control, the mRNA expression of orexigenic factor genes including neuropeptide Y (npy) and agouti-related protein (agrp) were significantly increased in larvae fed the diet with 0.005% GL, while the mRNA expression of anorexigenic factor genes including thyrotropin-releasing hormone (trh), cocaine and amphetamine regulated transcript (cart), and leptin receptor (lepr) were significantly decreased in larvae fed the diet with 0.005% GL (P < 0.05). The trypsin activity in larvae fed the diet with 0.005% GL was significantly higher than the control (P < 0.05). The alkaline phosphatase (AKP) activity in larvae fed the diet with 0.01% GL was significantly higher than the control (P < 0.05). A clear increase of total glutathione (T-GSH) content, activities of superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) was observed in larvae fed the diet with 0.01% GL compared with the control (P < 0.05). Moreover, the mRNA expression of interleukin-1β (il-1β) and interleukin-6 (il-6) (proinflammatory genes) in larvae fed the diet with 0.02% GL were significantly lower than the control (P < 0.05). In conclusion, the supplementation of 0.005% -0.01% GL could enhance the expression of orexigenic factor genes, activities of digestive enzymes and antioxidant capacity, ultimately improving the survival, and growth performance of large yellow croaker larvae.

Effects of supplemental ferulic acid (FA) on survival, growth performance, digestive enzyme activities, antioxidant capacity and lipid metabolism of large yellow croaker (Larimichthys crocea) larvae

A 30-day feeding trial was conducted to investigate the effects of supplemental ferulic acid (FA) on survival, growth performance, digestive enzyme activities, antioxidant capacity and lipid metabolism of the  large yellow croaker larvae (initial weight: 2.58 ± 0.30 mg). Four isonitrogenous and isolipidic micro-diets were formulated with graded levels of FA (0, 20, 40, and 80 mg/kg) and fed to the experimental larvae seven times daily. Results showed that larvae fed the diet with 40 mg/kg FA had significantly higher survival rate, while the specific growth rate was higher in larvae fed diets with 40 and 80 mg/kg FA than the control group (P < 0.05). Activities of trypsin in pancreatic segments (PS) and intestinal segments, lipase in PS and alkaline phosphatase in brush border membrane were significantly increased by supplementation of FA compared to the control group (P < 0.05). Supplementation of FA significantly increased activities of total superoxide dismutase and catalase, and reduced the malondialdehyde content compared to the control group (P < 0.05). Meanwhile, activities of lysozyme, total nitric oxide synthase and nitric oxide content were significantly improved by supplemental FA in diets. Furthermore, supplementation of 40 mg/kg FA reduced the triglyceride content in larval visceral mass probably through down-regulating expression of lipogenesis-related genes (scd1, fas and dgat2) and up-regulating expression of lipid catabolism-related genes (aco, cpt-1 and hl). In conclusion, appropriate supplementation of 40 mg/kg FA could improve the survival and growth performance of large yellow croaker larvae through increasing digestive function, antioxidant capacity and promoting lipid metabolism.

Activation of farnesoid X receptor suppresses ER stress and inflammation via the YY1/NCK1/PERK pathway in large yellow croaker (Larimichthys crocea)

Unfolded protein responses from endoplasmic reticulum (ER) stress have been implicated in inflammatory signaling. The vicious cycle of ER stress and inflammation makes regulation even more difficult. This study examined effects of farnesoid X receptor (FXR) in ER-stress regulation in large yellow croakers. The soybean-oil-diet-induced expression of ER stress markers was decreased in fish with FXR activated. In croaker macrophages, FXR activation or overexpression significantly reduced inflammation and ER stress caused by tunicamycin (TM), which was exacerbated by FXR knockdown. Further investigation showed that the TM-induced phosphorylation of PERK and EIF2α was inhibited by the overexpression of croaker FXR, and it was increased by FXR knockdown. Croaker NCK1 was then confirmed to be a regulator of PERK, and its expression in macrophages is increased by FXR overexpression and decreased by FXR knockdown. The promoter activity of croaker NCK1 was inhibited by yin-yang 1 (YY1). Furthermore, the results show that croaker FXR overexpression could suppress the P65-induced promoter activity of YY1 in HEK293t cells and decrease the TM-induced expression of yy1 in macrophages. These results indicate that FXR could suppress P65-induced yy1 expression and then increase NCK1 expression, thereby inhibiting the PERK pathway. This study may benefit the understanding of ER stress regulation in fish, demonstrating that FXR can be used in large yellow croakers as an effective target for regulating ER stress and inflammation.

Biotin alleviates hepatic and intestinal inflammation and apoptosis induced by high dietary carbohydrate in juvenile turbot (Scophthalmus maximus L.)

Excessive dietary carbohydrate commonly impairs the functions of liver and intestine in carnivorous fish. In the present study, a 10-week feeding trial was carried out to explore the regulation of biotin on the hepatic and intestinal inflammation and apoptosis in turbot (Scophthalmus maximus L.) fed with high carbohydrate diets. Three isonitrogenous and isolipidic experimental diets were designed as follows: the CC diet with 18.6% of carbohydrate and 0.04 mg/kg of biotin, the HC diet with 26.9% of carbohydrate and 0.05 mg/kg of biotin, and the HCB diet with 26.9% of carbohydrate and 1.62 mg/kg of biotin. Results showed that high dietary carbohydrate (HC diet) impaired the morphology of liver and intestine, however, inclusion of dietary biotin (HCB diet) normalized their morphology. Inflammation-related gene expression of nuclear factor κB p65 (nf-κb p65), tumor necrosis factor α (tnf-α), interleukin-1β (il-1β), il-6 and il-8, and the protein expression of NF-κB p65 in the liver and intestine were significantly up-regulated in the HC group compared to those in the CC group (P < 0.05), the HCB diet decreased their expression compared to the HC group (P < 0.05). The gene expression of il-10 and transforming growth factor-β (tgf-β) in the liver and intestine were significantly decreased in the HC group compared to the CC group (P < 0.05), and inclusion of dietary biotin increased the il-10 and tgf-β expression in the liver and intestine (P < 0.05). Moreover, compared to the CC group, the HC group had a stronger degree of DNA fragmentation and more TUNEL-positive cells in the liver and intestine, and the HCB group had a slighter degree of DNA fragmentation and fewer TUNEL-positive cells compared to the HC group. Meanwhile, the gene expression of B-cell lymphoma protein-2-associated X protein (bax) and executor apoptosis-related cysteine peptidase 3 (caspase-3) were significantly up-regulated and the gene expression of B-cell lymphoma-2 (bcl-2) was significantly down-regulated both in the liver and intestine in the HC group compared with those in the CC group (P < 0.05). Inclusion of dietary biotin significantly decreased the bax and caspase-3 mRNA levels and increased bcl-2 mRNA level in the liver and intestine (P < 0.05). In conclusion, high dietary carbohydrate (26.9% vs 18.6%) induced inflammation and apoptosis in liver and intestine. Supplementation of biotin (1.62 mg/kg vs 0.05 mg/kg) in diet can alleviate the high-dietary-carbohydrate-induced hepatic and intestinal inflammation as well as inhibit apoptosis in turbot. The present study provides basic data for the application of biotin into feed, especially the high-carbohydrate feed for turbot.

Effects of replacing dietary fish meal with enzyme-treated soybean meal on growth performance, intestinal microbiota, immunity and mTOR pathway in abalone Haliotis discus hannai

In addition to eliminating most of the anti-nutritional factors in soybean meal, enzyme-treated soybean meal (ESBM) can also increase the proportion of small peptides. It was found that ESBM can replace fish meal (FM) either partially or completely in diets for some fish and shrimp species. In the present study, the effects of replacing dietary FM with ESBM on growth performance, intestinal microbiota, immunity and mTOR pathway in abalone Haliotis discus hannai (initial weight: 16.75 ± 0.09 g) were investigated after a 100-day feeding trial. Five experimental diets were designed to replace 0%, 25%, 50%, 75% and 100% of dietary FM by ESBM, which were named as ESBM0 (control), ESBM25, ESBM50, ESBM75 and ESBM100, respectively. Results showed that ESBM could replace up to 75% of FM in the diet without significant effect on the weight gain rate (WGR, 118.05%-124.16%) of abalone. The increasing dietary ESBM levels significantly decreased the trypsin activity from 418.52 to 286.52 U/mg protein in the digestive gland. No significant differences in the contents of total cholesterol (T-CHO), ammonia (BLA) and malondialdehyde (MDA) in cell-free hemolymph were observed among the groups with replacement levels of dietary FM by ESBM from 0% to 75%. Excessive replacement level of FM with ESBM (ESBM100) significantly increased the MDA content (2.33 nmol/mg prot.) and pro-inflammatory-related gene expression in digestive gland. Compared with the control group, the mTOR pathway in muscle was significantly upregulated in the ESBM75 group. The digestive gland in the ESBM100 group contained more golden refractile spherules than those in the other groups. The abundance of intestinal microbes such as Halomonas, Zobellella and Bacillus was decreased in the ESBM100 group. In conclusion, up to 75% of replacement of dietary FM by ESBM had no negative effects on the growth performance, intestinal microbiota, immunity and mTOR pathway of abalone.

Role of acyl-coenzyme A oxidase 1 (ACOX1) on palmitate-induced inflammation and ROS production of macrophages in large yellow croaker (Larimichthys crocea)

Acyl-coenzyme A oxidase 1 (ACOX1) is the rate-limiting enzyme in peroxisomal β-oxidation, and it plays an essential role in mediating the inflammatory response and reactive oxygen species (ROS) metabolism in mammals. However, the role of ACOX1 in fish has not been completely elucidated. Herein, this study was conducted to investigate the role of large yellow croaker (Larimichthys crocea) ACOX1 (Lc-ACOX1) on palmitate (PA)-induced inflammation and ROS production. In this study, Lc-ACOX1 was cloned and characterized. The full-length CDS of Lc-acox1 was 1986 bp, encoding 661 amino acids. Tissue distribution results showed that the gene expression of Lc-acox1 was the highest in the intestine and the lowest in the spleen. Moreover, results showed that the mRNA expression of Lc-acox1 was upregulated by PA, with elevated pro-inflammatory gene expression, including il-1β, il-6, il-8, tnf-α, cox2 and ifn-γ, as well as ROS content in macrophages of large yellow croaker. Furthermore, the role of Lc-ACOX1 in inflammation induced by PA was investigated by using the ACOX1 inhibitor TDYA. Treatment of macrophages with TDYA reduced the mRNA expression of pro-inflammatory genes induced by PA. Moreover, inhibition of ACOX1 reduced the elevated level of ROS caused by PA and increased the mRNA expression of antioxidant genes. In conclusion, this study first identified that fish ACOX1 was involved in the PA-induced inflammatory response and ROS production.

Additional supplementation of sulfur-containing amino acids in the diets improves the intestinal health of turbot fed high-lipid diets

An eight-week feeding trial was conducted to investigate the effects of diets supplemented with three sulfur-containing amino acids (SAA), namely, methionine, cysteine, and taurine, on the intestinal health status of juvenile turbot (Scophthalmus maximus) fed high-lipid diets. Four diets were formulated, namely, a high-lipid control diet (16% lipid, HL) and three SAA-supplemented diets, which were formulated by supplementing 1.5% methionine (HLM), 1.5% cysteine (HLC), and 1.5% taurine (HLT) into the HL control diet, respectively. Each diet was assigned to triplicate tanks, and each tank was stocked with 30 juvenile fish (appr. initial weight, 8 g). The histological and morphometric results showed that dietary SAA supplementation obviously improved the intestinal morphology and integrity, in particular as reflected by higher height of microvilli and mucosal folds. Dietary SAA supplementation, in particular cysteine, up-regulated the gene expression of mucin-2 and tight junction proteins (ZO-1, Tricellilun and JAM). Dietary SAA supplementation remarkably down-regulated the gene expression of apoptosis-related factors such as p38, JNK, and Bax, expression of pro-inflammatory factors (e.g., NF-κB, AP-1 IL-1β, IL-8, and TNF-α). SAA supplementation resulted in higher antioxidative abilities in the intestine. Additionally, dietary SAA supplementation largely altered the communities of intestinal microbiota. Compared with the HL group, higher relative abundance of potential beneficial bacteria, and lower relative abundance of opportunistic pathogens were observed in SAA-supplemented groups. Dietary taurine supplementation significantly increased the relative abundance of Ligilactobacillus (in particular Lactobacillus murinus) and Limosilactobacillus (especially Lactobacillus reuteri). In conclusion, dietary sulfur-containing amino acids supplementation have promising potential in ameliorating the intestinal inflammation of turbot fed high-lipid diets. Especially dietary cysteine and taurine supplementation have more positive effects on the communities of the intestinal microbiota of turbot.

Effects of recombinant anti-lipopolysaccharide factor expressed by Pichia pastoris on the growth performance, immune response and disease resistance of Litopenaeusvannamei

The codon-optimized anti-lipopolysaccharide factor (ALF) sequence was introduced into pPICZαA vector and transformed into Pichia pastoris GS115. The recombinant ALF yeast supernatant (rALF-mix) was freeze-dried and evaluated as a feed additive for Litopenaeus vannamei. It was found by antibacterial activity test in vitro that the rALF-mix had antibacterial activity under different pH and temperature conditions. The 0, 0.00375%, 0.0075%, 0.015%, 0.03% and 0.06% of rALF-mix were added respectively to make the six experimental diets. After a 10-week feeding trial with shrimps (2.36 ± 0.02 g), it was found that the weight gain rate (WGR) and protein efficiency ratio (PER) of shrimp in the groups with 0.0075%, 0.015% and 0.03% of dietary rALF-mix supplementation were significantly higher than those in the control group (P < 0.05). Dietary rALF-mix supplementation significantly increased the total haemocyte count, respiratory burst, phagocytic activity, total anti-oxidative capacity (T-AOC), phenol oxidase activity, nitric oxide synthase activity, lysozyme (LYZ) activity, serum antibacterial capacity in the hemolymph and the T-AOC, LYZ in the hepatopancreas of shrimps (P < 0.05). The malondialdehyde contents in hemolymph and hepatopancreas were significantly decreased (P < 0.05). Meanwhile, the expression levels of toll, immune deficiency, heat shock protein 70, crustin and lipopolysaccharide-β-glucan binding protein in the gill of shrimps were significantly increased (P < 0.05). After the challenge test, it was showed that dietary rALF-mix supplementation significantly improved the resistance of L. vannamei to Vibrio parahaemolyticus (P < 0.05). In conclusion, the rALF-mix can be used as a functional feed additive to improve the growth, immunity and disease resistance of shrimp. Based on the quadratic regression analysis for WGR, the optimal supplemental level of rALF-mix in diet for shrimp was estimated to be 0.02813%.

Replacement of Dietary Fishmeal Protein with Degossypolized Cottonseed Protein on Growth Performance, Nonspecific Immune Response, Antioxidant Capacity, and Target of Rapamycin Pathway of Juvenile Large Yellow Croaker (Larimichthys crocea)

A 70-day feeding experiment was carried out to assess the replacement of dietary fishmeal (FM) protein with degossypolized cottonseed protein (DCP) on large yellow croaker (Larimichthys crocea) with initial body weight (13.09 ± 0.50 g). Five isonitrogenous and isolipidic diets replaced fishmeal protein with 0%, 20%, 40%, 60%, and 80% DCP were formulated and named as FM (the control group), DCP20, DCP40, DCP60, and DCP80, respectively. Results displayed that weight gain rate (WGR) and specific growth rate (SGR) in the DCP20 group (263.91% and 1.85% d^-1) were significantly increased compared with the control group (194.79% and 1.54% d^-1) (P < 0.05). Furthermore, fish fed the diet with 20% DCP significantly increased the activity of hepatic superoxide dismutase (SOD) compared with the control group (P < 0.05). Meanwhile, the content of hepatic malondialdehyde (MDA) in the DCP20, DCP40, and DCP80 groups was significantly lower than that in the control group (P < 0.05). The activity of intestinal trypsin in the DCP20 group was significantly degraded compared with that in the control group (P < 0.05). The transcription of hepatic proinflammatory cytokine genes (interleukin-6 (il-6); tumor necrosis factor-α (tnf-α); and interferon-γ (ifn-γ)) in the DCP20 and DCP40 groups was significantly upregulated compared with that in the control group (P < 0.05). As to the target of rapamycin (TOR) pathway, the transcription of hepatic target of rapamycin (tor) and ribosomal protein (s6) was significantly up-regulated, while the transcription of hepatic eukaryotic translation initiation factor 4E binding protein 1 (4e-bp1) gene was significantly downregulated in the DCP group compared with the control group (P < 0.05). In summary, based on the broken line regression model analysis of WGR and SGR against dietary DCP replacement levels, the optimal replacement level was recommended to be 8.12% and 9.37% for large yellow croaker, respectively. These results revealed that FM protein replaced with 20% DCP could promote digestive enzyme activities and antioxidant capacity and further activate immune response and the TOR pathway so that growth performance of juvenile large yellow croaker was improved.