Cloning and characterization of fatty acid-binding proteins (fabps) from Japanese seabass (Lateolabrax japonicus) liver, and their gene expressions in response to dietary arachidonic acid (ARA)

Subchronic oral exposure to polystyrene microplastics affects hepatic lipid metabolism, inflammation, and oxidative balance in gilthead seabream (Sparus aurata)

Microplastics (MPs) pose a clear threat to aquatic organisms affecting their health. Their impact on liver homeostasis, as well as on the potential onset of nonalcoholic fatty liver disease (NAFLD), is still poorly investigated and remains almost unknown. The aim of this study was to evaluate the outcomes of subchronic exposure to polystyrene MPs (PS-MPs; 1-20 μm; 0, 25, or 250 mg/kg b.w./day) on lipid metabolism, inflammation, and oxidative balance in the liver of gilthead seabreams (Sparus aurata Linnaeus, 1758) exposed for 21 days via contaminated food. PS-MPs induced an up-regulation of mRNA levels of crucial genes associated with lipid synthesis and storage (i.e., PPARy, Srebp1, Fasn) without modifications of genes involved in lipid catabolism (i.e., PPARα, HL, Pla2) or transport and metabolism (Fabp1) in the liver. The increase of CSF1R and pro-inflammatory cytokines gene expression (i.e., TNF-α and IL-1β) was also observed in exposed fish in a dose-dependent manner. These findings were confirmed by hepatic histological evaluations reporting evidence of lipid accumulation, inflammation, and necrosis. Moreover, PS-MPs caused the impairment of the hepatic antioxidant defense system through the alteration of its enzymatic (catalase, superoxide dismutase, and glutathione reductase) and non-enzymatic (glutathione) components, resulting in the increased production of reactive oxygen species (ROS) and malondialdehyde (MDA), as biomarkers of oxidative damage. The alteration of detoxifying enzymes was inferred by the decreased Ethoxyresorufin-O-deethylase (EROD) activity and the increased activity of glutathione-S-transferase (GST) at the highest PS-MP dose. The study suggests that PS-MPs affect the liver health of gilthead seabream. The liver dysfunction and damage caused by exposure to PS-MPs result from a detrimental interplay of inflammation, oxidative damage, and antioxidant and detoxifying enzymatic systems modifications, altering the gut-liver axis homeostasis. This scenario is suggestive of the involvement of MP-induced effects in the onset and progression of hepatic lipid dysfunction in gilthead seabream.

Transcriptome analysis revealed potential mechanisms of channel catfish growth advantage over blue catfish in a tank culture environment

Channel catfish (Ictalurus punctatus) and blue catfish (Ictalurus furcatus) are two economically important freshwater aquaculture species in the United States, with channel catfish contributing to nearly half of the country's aquaculture production. While differences in economic traits such as growth rate and disease resistance have been noted, the extent of transcriptomic variance across various tissues between these species remains largely unexplored. The hybridization of female channel catfish with male blue catfish has led to the development of superior hybrid catfish breeds that exhibit enhanced growth rates and improved disease resistance, which dominate more than half of the total US catfish production. While hybrid catfish have significant growth advantages in earthen ponds, channel catfish were reported to grow faster in tank culture environments. In this study, we confirmed channel fish's superiority in growth over blue catfish in 60-L tanks at 10.8 months of age (30.3 g and 11.6 g in this study, respectively; p < 0.001). In addition, we conducted RNA sequencing experiments and established transcriptomic resources for the heart, liver, intestine, mucus, and muscle of both species. The number of expressed genes varied across tissues, ranging from 5,036 in the muscle to over 20,000 in the mucus. Gene Ontology analysis has revealed the functional specificity of differentially expressed genes within their respective tissues, with significant pathway enrichment in metabolic pathways, immune activity, and stress responses. Noteworthy tissue-specific marker genes, including lrrc10, fabp2, myog, pth1a, hspa9, cyp21a2, agt, and ngtb, have been identified. This transcriptome resource is poised to support future investigations into the molecular mechanisms underlying environment-dependent heterosis and advance genetic breeding efforts of hybrid catfish.

Fatty acid-binding protein genes in gilthead seabream: molecular cloning and nutritional regulation under low water temperatures

The molecular characteristics and tissue disruption of 10 fatty acid-binding protein (fabp) genes in gilthead seabream (Sparus aurata) were investigated, and their expression levels were found in the fish fed diets with different vegetable oil (VO) sources, which may explore the potential function of fabp genes in S. aurata. For this purpose, the open reading frames of fabp genes involved in the transport and ß-oxidation of fatty acids (FA) were molecularly cloned and characterized. S. aurata was then exposed to a two-staged feeding trial (the grow-out period following a wash-out period) at low water temperatures. In the grow-out period, the fish were fed diets containing 50% and 100% ratios of various VOs for 60 days, and in the wash-out period, the fish were fed a diet containing 100% fish oil (FO) for 30 days. It has been determined that (a) S. aurata and vertebrate fabp/FABP genes are orthologues; (b) spatio-temporal differences in tissue-specific patterns of fabp genes differ importantly; for instance, the difference between the highest and lowest values reaches 13 × 10⁵ -fold in the fabp10a; and (c) VO-based diets upregulated fabp transcript levels in the liver and muscle with some exceptions, such as liver fabp11a and muscle fabp7a. Gene expressions of only the hepatic fabp7b and fabp10a genes were diminished at the end of the wash-out period. In this study, the authors provide further evidence that dietary FAs affect fabp mRNA expressions in S. aurata. This might be useful in the nutritional control of fabp genes to maintain lipid homeostasis in marine fish fed VO-based diets at low water temperatures.

Environmental concentrations of benzophenone-3 disturbed lipid metabolism in the liver of clown anemonefish (Amphiprion ocellaris)

Benzophenone-3 (BP-3) often used as a UV filter in various products and an endocrine disruptor. In this work, we exposed the clown anemonefish to 10 μg/L and 50 μg/L BP-3 for 7 and 14 days. Liver histological, biochemical analysis, and transcriptome sequencing were used to explore the mechanism of the lipid metabolism disorder in the liver of three-month-old clown anemonefish treated with BP-3. The histological and biochemical analysis showed that BP-3 induces morphological changes and lipid droplet accumulation, and the lipid content, lipase, and antioxidant enzyme activity were abnormal. After treatment with 10 μg/L and 50 μg/L BP-3 for 7 days, the transcriptome analysis further demonstrated that the KEGG analysis revealed that the differentially expressed genes (DEGs) were mainly associated with fat digestion and absorption, PPAR signaling pathway, circadian rhythm, and mineral absorption pathways; After 10 μg/L and 50 μg/L of BP-3 exposure for 14 days, the KEGG analysis were mainly associated with circadian rhythm, circadian rhythm-fly, protein processing in the endoplasmic reticulum, and beta-alanine metabolism pathways. Several key genes were involved in the process of liver lipid metabolism, including CD36, APoA-Ⅰ, FABP, LPL, ACS, and PEPCK. The qRT-PCR validation results showed that eight genes (CYP8B1, FABP1, LPL, MGAT, PEPCK, PER1, PSMB4, PSME2) were significantly down-regulated, and the other two genes (Fbxl3, RXR) were significantly up-regulated after 7 days of BP-3 exposure. Similarly, eleven genes (AMPK, ARNTL, Bmal1, CASP3, CYC, CYP2J, CYP2U1, GSK3A, PEPCK, RAC1, RORA) were significantly up-regulated, and the other four genes (NR1D1, PER1, PTGDS, HLF) were significantly down-regulated after 14 days of BP-3 exposure. In conclusion, our results elucidate the physiological and molecular responses to BP-3 exposure in the liver lipid metabolism of clown anemonefish, and these findings reveal that the regulation of lipid metabolism is disturbed when clown anemonefish is exposed to UV filters.

Fabp4 contributes toward regulating inflammatory gene expression and oxidative stress in Ctenopharyngodon idella

Fatty acid-binding protein (Fabp)-4 is a member of the FABP family. Mammalian fabp4 has been demonstrated to involve in inflammation and immunity, whereas the related data of fish fabp4 remain limited. Therefore, we further investigated the effects of fabp4 on immunity in Ctenopharyngodon idella. The fabp4 sequence spanned 405 bp was cloned first, sharing high identity to fabp4 from other fish and mammals. Fabp4 expression was the highest in the adipose tissue, followed by the heart, muscle, and liver. In vivo, lipopolysaccharide (LPS) triggered the expression of fabp4, toll-like receptor (tlr)-22, interleukin (il)-1β, and tumor necrosis factor (tnf)-α in the kidney and spleen. In vitro, exposing C. idella CIK cells to LPS decreased their viability, and the expression of fabp4 was also increased by LPS. However, BMS309403, an inhibitor of FABP4, mitigated these effects. Furthermore, treating the cells with LPS or fabp4 overexpression plasmids resulted in reactive oxygen species (ROS) generation and upregulation of inflammatory genes expression, including tlr22, type-I interferon (ifn-1), interferon regulatory factor (irf)-7, tnfα, il-1β, and interferon-β promoter stimulator 1. These effects were ameliorated by preincubation with BMS309403. Moreover, incubating the cells with glutathione reduced the production of ROS and the expression of inflammatory genes that were evoked by LPS and plasmid treatments. These results showed that fabp4 acts as a pro-inflammatory molecule via elevating ROS levels, providing a novel understanding of the molecular regulation of innate immunity in teleosts.

PPARγ regulates fabp4 expression to increase DHA content in golden pompano (Trachinotus ovatus) hepatocytes

N-3 long-chain (≥C20) PUFA (LC-PUFA) are vital fatty acids for fish and humans. As a main source of n-3 LC-PUFA for human consumers, the n-3 LC-PUFA content of farmed fish is important. Previously, we identified fatty acid-binding protein (fabp)-4 as a candidate gene for regulating the n-3 LC-PUFA content. Herein, we further assessed the role of fabp4 in this process. First, a 2059 bp promoter sequence of fabp4 in Trachinotus ovatus was cloned and, using progressive deletion, determined -2006 bp to -1521 bp to be the core promoter sequence. The PPAR-γ binding sites were predicted to occur in this region. A luciferase reporter assay showed that the promoter activity of fabp4 decreased following mutation of the PPARγ binding site and that PPARγ increased the fabp4 promoter activity in a dose-dependent manner, implying that T. ovatus fabp4 is a target of PPARγ. The overexpression of fabp4 or PPARγ increased the DHA content in hepatocytes, whereas suppression of their expression diminished this effect, suggesting that both fabp4 and PPARγ play an active role in regulating DHA content. Moreover, the inhibition of fabp4 attenuated the increase in PPARγ-mediated DHA content, and the overexpression of fabp4 alleviated this effect. Collectively, our findings indicated that fabp4, which is controlled by PPARγ, plays an important role in DHA content regulation. The new regulation axis can be considered a promising novel target for increasing the n-3 LC-PUFA content in T. ovatus.

Molecular cloning, tissue expression, and transcriptional regulation of fabp1 and fabp2 in javelin goby (Synechogobius hasta) in response to starvation stress

Fatty acid binding proteins (FABPs) are intracellular lipid chaperones with low molecular weight, which are widely distributed in a variety of tissues, participating in fatty acid transport, cell proliferation, and angiogenesis. In this study, full-length sequences of two fabp genes (fabp1 and fabp2) from javelin goby (Synechogobius hasta) were cloned via RACE PCR, followed by bioinformatic analyses and gene expression evaluation. The fabp1 and fabp2 cDNA sequences were 493 and 626 bp in length, encoding 126 and 132 amino acids, respectively. Phylogenetic analysis revealed that both genes from S. hasta were clustered with those of other fish species in accordance with their known taxonomic relationships. fabp1 and fabp2 mRNA showed distinct expression patterns in different tissues, with fabp1 being most expressed in the liver and fabp2 in the intestine. Furthermore, the expression of fabp1 in the liver was significantly up-regulated during starvation, whereas fabp2 mRNA level in the intestine initially increased and then decreased, indicating that the transcriptional responses of the two genes could be influenced by malnourishment/starvation. Changes in the transcriptional levels of fabp1 and fabp2 also suggested that glycogen was catabolized in the liver of S. hasta at the beginning of starvation prior to lipid depletion, whereas lipids served as fuel reserves in the intestine during short-term starvation. In conclusion, this study provides fundamental insights into the role of Fabps in S. hasta lipid metabolism.

Cloning, molecular characterization, and nutritional regulation of fatty acid-binding protein family genes in gold pompanos (Trachinotus ovatus)

Fatty acid-binding protein (Fabp) is an important protein family involved in fatty acid uptake and deposition. Elucidating the function and regulation of fabps could contribute to the efficient production of biologically relevant fatty acids, such as highly unsaturated fatty acids (HUFAs), from fish. Herein, five genes from Trachinotus ovatus named fabp4, fabp6a, fabp6b, fabp7a, and fabp7b coding 133, 127, 118, 132, and 132 amino acid residues were cloned and sequenced. The effect of dietary HUFA on the expression of these genes was also investigated. Multiple protein sequence alignment showed that these Fabps shared high identity to their orthologs from other fish and mammals. Two conserved domains, lipocalin and lipocalin 7, were predicted in the deduced protein sequence of fabp4 and fabp7 paralogs, whereas fabp6 paralogs did not present the lipocalin domain. The adipose tissue, spleen, gill, and intestine showed the highest levels of fabp6b expression. In the brain, fabp6b was weakly expressed, whereas the expression of fabp7a was at its highest. Conversely, fabp7a showed a lower mRNA level than the other fabps in the liver and heart. In the dorsal muscle and kidney, fabp6a was the most abundantly expressed gene. Increasing dietary HUFA from 1.0% to 2.1% increased the gene expression of hepatic fabp4 and fabp6a gene expression but decreased gene expression in the dorsal muscle. Similarly, the expression of fabp7a in the dorsal muscle also declined in the 2.1% HUFA group. This study lays the groundwork for further studies focused on the physiological function and regulation of fish fabps.

Transcriptome analysis of golden pompano (Trachinotus ovatus) liver indicates a potential regulatory target involved in HUFA uptake and deposition

Promoting highly unsaturated fatty acid (HUFA) uptake and deposition can improve nutritional value of farmed fish and reduce dietary fish oil addition. Previously, we found that the golden pompano Trachinotus ovatus liver HUFA content increased with the increasing of dietary HUFA. Therefore, we examined the common genes and pathways responsible for HUFA uptake and deposition in T. ovatus liver using transcriptome sequencing technology after feeding with either 1.0% or 2.1% HUFA for 8 weeks. Results showed that a total of 140 and 147 genes were significantly upregulated and downregulated, respectively. Five bile acid synthesis-related genes (CYP7A1, CYP8B1, AKR1D1, SCP2 and ACOT8), which are related to dietary fat emulsification were downregulated in 2.1% HUFA group, implying that the cholate synthesized through the classical pathway might be the main bile acid form in fat emulsification. Moreover, fatty acid transport protein (FATP)-6, fatty acid binding protein (FABP)-1, -4, and -6 increased with HUFA deposition, especially FATP6 and FABP4, suggesting that the two genes may be important mediators involved in HUFA uptake and deposition. KEGG analysis showed that most of the differential genes described above were involved in peroxisome proliferator activator receptor (PPAR) signaling pathway, and PPARγ increased with HUFA deposition, indicating that PPARγ might be a key regulator of HUFA uptake and deposition by regulating the genes involved in fatty acid emulsification and transport. This study focused on the liver, which is the center of intermediary metabolism, providing a comprehensive understanding of the molecular regulation of HUFA uptake and deposition in T. ovatus, which should be further investigated to develop potential measures to improve HUFA content.

Hepatic transcriptome of the euryhaline teleost Japanese seabass (Lateolabrax japonicus) fed diets characterized by α-linolenic acid or linoleic acid

To investigate the different effects of dietary α-linolenic acid (ALA) and linoleic acid (LA) on the euryhaline fish Japanese seabass, a feeding trial followed by hepatic transcriptome assay was conducted. Two experimental diets containing 10% LA-rich sunflower seed oil (diet LA) or 10% ALA-rich perilla oil (diet ALA) were used in the feeding trial. LA and ALA in diets were characteristically incorporated into fish tissues while no significant difference was observed in growth performance and body proximate composition between groups LA and ALA. Compared to LA, ALA up-regulated transcription of 49 unigenes and down-regulated those of 311 unigenes. Quantitative RT-PCR studies on eight lipid metabolism-related genes and seven randomly selected genes were conducted to validate the transcriptomic results. Lipid metabolism-related genes ApoA1, ApoA4, ApoE, FABP1, FABP3, FABP4, FATP6, and DGAT1, as well as ribosomal proteins L9e, L13e, and S4e, were transcriptionally down-regulated by ALA. The differentially expressed genes (DEGs) were primarily enriched in Gene Ontology terms such as Lipid transport, Protein metabolic process, and Ribosome biogenesis, as well as in KEGG pathways such as Complement and coagulation cascades and Ribosome. The Protein-Protein Interaction (PPI) network based on the peptide biosynthesis-related DEGs showed that ribosomal proteins such as SAe, L4e, S4e, L15e, L9e, and L13Ae had high betweenness centrality in the dietary regulation of peptide biosynthetic processes. In conclusion, under the present experimental conditions, a high level of dietary α-linolenic acid tended to suppress lipid transport and protein biosynthetic processes in the liver of Japanese seabass at the gene expression level.

Moderate levels of dietary arachidonic acid reduced lipid accumulation and tended to inhibit cell cycle progression in the liver of Japanese seabass Lateolabrax japonicus

To investigate the physiological roles of dietary arachidonic acid (ARA) in fish, a feeding trial with Japanese seabass was conducted, followed by a hepatic transcriptome assay. Six experimental diets differing basically in ARA level (0.05%, 0.22%, 0.37%, 0.60%, 1.38% and 2.32% of dry matter) were used in the feeding trial. Liver samples from fish fed diets with 0.05% and 0.37% ARA were subjected to transcriptomic assay, generating a total of 139 differently expressed unigenes, which were primarily enriched in lipid metabolism and cell cycle-related signaling pathways. Then, qRT-PCR validation on lipid metabolism and cell cycle-related genes as well as corresponding enzyme-linked immunosorbent assay of selected proteins were conducted with liver samples from all six groups. Moderated ARA levels reduced lipogenesis and stimulated β-oxidation concurrently, but high ARA levels seemed to affect lipid metabolism in complicated ways. Both gene expression and protein concentration of cell cycle-related proteins were decreased by moderate levels of dietary ARA. The lipid content and fatty acid composition in fish confirmed the transcription and protein concentration results related to lipid metabolism. In conclusion, moderate levels of dietary ARA (0.37% and 0.60%) reduced lipid accumulation and tended to inhibit cell cycle progression in the liver of Japanese seabass.

Molecular cloning and tissue distribution of fatty acid binding protein-3 in goldfish (Carassius auratus) and its mRNA expression in response to cadmium and PAMPs

Fatty acid binding proteins (FABPs) are members of the conserved, multigene family of intracellular lipid binding proteins. In this study, the full-length cDNA of goldfish (Carassius auratus) FABP-3 (gfFABP-3) was successfully cloned. gfFABP-3 had an open reading frame of 402 bp and encoded a 133 amino acid polypeptide. The predicted gfFABP-3 protein included a lipocalin domain and displayed typical conserved FABP tertiary structures. Reverse transcription-PCR (RT-PCR) revealed that the gfFABP-3 gene was expressed in all tested tissues, with higher levels of expression in the testis, liver, heart, fat and kidney. After 24 h of cadmium exposure, gfFABP-3 was significantly upregulated in the gill, liver and spleen, but downregulated in the intestine, as compared to unexposed controls. gfFABP-3 expression was significantly downregulated in the spleen in goldfish challenged with LPS and Poly I:C. Our study provides a molecular characterization of goldfish FABP-3 and indicated that gfFABP-3 was potentially associated with the toxic effects of cadmium on lipid metabolism, and with the immune response to pathogenic infection.