Transcriptome analysis reveals that high temperatures alter modes of lipid metabolism in juvenile turbot (Scophthalmus maximus) liver

Lipid Metabolic Disorders Induced by Organophosphate Esters in Silver Carp from the Middle Reaches of the Yangtze River

The Yangtze River fishery resources have declined strongly over the past few decades. One suspected reason for the decline in fishery productivity, including silver carp (Hypophthalmichthys molitrix), has been linked to organophosphate esters (OPEs) contaminant exposure. In this study, the adverse effect of OPEs on lipid metabolism in silver carp captured from the Yangtze River was examined, and our results indicated that muscle concentrations of the OPEs were positively associated with serum cholesterol and total lipid levels. In vivo laboratory results revealed that exposure to environmental concentrations of OPEs significantly increased the concentrations of triglyceride, cholesterol, and total lipid levels. Lipidome analysis further confirmed the lipid metabolism dysfunction induced by OPEs, and glycerophospholipids and sphingolipids were the most affected lipids. Hepatic transcriptomic analysis found that OPEs caused significant alterations in the transcription of genes involved in lipid metabolism. Pathways associated with lipid homeostasis, including the peroxisome proliferator-activated receptor (PPAR) signal pathway, cholesterol metabolism, fatty acid biosynthesis, and steroid biosynthesis, were significantly changed. Furthermore, the affinities of OPEs were different, but the 11 OPEs tested could bind with PPARγ, suggesting that OPEs could disrupt lipid metabolism by interacting with PPARγ. Overall, this study highlighted the harmful effects of OPEs on wild fish and provided mechanistic insights into OPE-induced metabolic disorders.

pparβ regulates lipid catabolism by mediating acox and cpt-1 genes in Scophthalmus maximus under heat stress

Peroxisome proliferator-activated receptor β (pparβ) is a key gene-regulating lipid metabolism pathway, but its function in turbot remains unclear. In this study, the CDS of pparβ was cloned from kidney for the first time. The CDS sequence length was 1533 bp encoding 510 amino acids. Structural analysis showed that the pparβ protein contained a C4 zinc finger and HOLI domain, suggesting that the pparβ gene of turbot has high homology with the PPAR gene of other species. The high expression patterns of pparβ, acox, and cpt-1 at high temperatures, as shown through qPCR, indicated that high temperatures activated the transcriptional activity of pparβ and increased the activity of the acox and cpt-1 genes. The expression of acox and cpt-1 was significantly inhibited when pparβ was downregulated using RNAi technology and inhibitor treatments, suggesting that pparβ positively regulated acox and cpt-1 expression at high temperatures and, thus, modulates lipid catabolism activity. These results demonstrate that pparβ is involved in the regulation of lipid metabolism at high temperatures and expand a new perspective for studying the regulation of lipid metabolism in stress environments of teleost.

Effects of thermal stress responses in goldfish (Carassius auratus): growth performance, total carotenoids and coloration, hematology, liver histology, and critical thermal maximum

The present study aimed to investigate the effect of thermal stress on growth, feed utilization, coloration, hematology, liver histology, and critical thermal maximum (CTmax) in goldfish (Carassius auratus) cultured at three different acclimation temperatures including 27 °C, 30 °C, and 34 °C for 10 weeks. Goldfish were assigned randomly to tanks with a quadruplicate setup, accommodating 20 fish per tank. The result showed that fish acclimated to different temperatures did not significantly differ in weight gain (WG) and specific growth rate (SGR). However, increasing temperature significantly decreased feed efficiency ratio (FER), protein efficiency ratio (PER), and protein productive value (PPV), but significantly increased feed conversion ratio (FCR) (P < 0.05). The coloration parameters significantly decreased by high temperature in the trunk region with increasing temperature (L* and a* at week 5; L*, a*, and b* at week 10; P < 0.05). Total carotenoid contents in serum, fin, muscle, and skin also significantly decreased with increasing temperature (P < 0.05). Total protein, albumin, and globulin levels exhibited a notable decrease, while the albumin: globulin ratio showed a slight insignificant increase, with increasing temperature. Aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), total cholesterol, and triglycerides significantly increased with increasing temperature (P < 0.05). While, high-density lipoprotein cholesterol (HDL-c) decreased linearly (P < 0.05). Glucose and cortisol levels linearly increased with increasing temperature, the highest levels being observed in the 34 °C group. Liver histology showed swollen hepatocytes, nuclei displacement, and infiltration of inflammation in fish cultured at 34 °C. Goldfish acclimated to 34 °C displayed a higher CTmax of 43.83 °C compared to other groups. The present study showed that temperature should be kept below 34 °C for goldfish culture to prevent high FCR, fading coloration, and liver damages.

Comparative Transcriptomic Analysis of Largemouth Bass (Micropterus salmoides) Livers Reveals Response Mechanisms to High Temperatures

High temperatures are considered one of the most significant limitations to subtropical fishery production. Largemouth bass (Micropterus salmoides) is an economically important freshwater species grown in subtropical areas, which are extremely sensitive to heat stress (HS). However, comprehensive transcriptomic data for the livers of largemouth bass in response to HS are still lacking. In this study, a comparative transcriptomic analysis was performed to investigate the gene expression profiles of the livers of largemouth bass under HS treatment. As a result, 6114 significantly differentially expressed genes (DEGs), which included 2645 up-regulated and 3469 down-regulated genes, were identified in response to HS. Bioinformatics analyses demonstrated that the 'ECM-receptor interaction' pathway was one of the most dramatically changed pathways in response to HS, and eight DEGs assigned to this pathway were taken as hub genes. Furthermore, the expression of these eight hub genes was determined by quantitative reverse transcription PCR, and all of them showed a significant change at the transcriptional level, suggesting a crucial role of the 'ECM-receptor interaction' pathway in the response of largemouth bass to HS. These findings may improve our understanding of the molecular mechanisms underlying the response of largemouth bass to HS.

Stress responses to warming in Japanese flounder (Paralichthys olivaceus) from different environmental scenarios

Japanese flounder (Paralichthys olivaceus) is one of cold-water species widely farmed in Asia. In recent years, the increased frequency of extreme weather events caused by global warming has led to serious impact on Japanese flounder. Therefore, it is crucial to understand the effects of representative coastal economic fish under increasing water temperature. In this study, we investigated the histological and apoptosis responses, oxidative stress and transcriptomic profile in the liver of Japanese flounder exposed to gradual temperature rise (GTR) and abrupt temperature rise (ATR). The histological results showed liver cells in ATR group were the most serious in all three groups including vacuolar degeneration and inflammatory infiltration, and had more apoptosis cells than GTR group detected by TUNEL staining. These further indicated ATR stress caused more severe damage than GTR stress. Compared with control group, the biochemical analysis showed significantly changes in two kinds of heat stress, including GPT, GOT and D-Glc in serum, ATPase, Glycogen, TG, TC, ROS, SOD and CAT in liver. In addition, the RNA-Seq was used to analyze the response mechanism in Japanese flounder liver after heat stress. A total of 313 and 644 differentially expressed genes (DEGs) were identified in GTR and ATR groups, respectively. Further pathway enrichment of these DEGs revealed that heat stress affected cell cycle, protein processing and transportation, DNA replication and other biological processes. Notably, protein processing pathway in the endoplasmic reticulum (ER) was enriched significantly in KEGG and GSEA enrichment analysis, and the expression of ATF4 and JNK was significantly up-regulated in both GTR and ATR groups, while CHOP and TRAF2 were high expressed in GTR and ATR groups, respectively. In conclusion, heat stress could cause tissue damage, inflammation, oxidative stress and ER stress in the liver of Japanese flounder. The present study would provide insight into the reference for the adaptive mechanisms of economic fish in face of increasing water temperature caused by global warming.

Genome-Wide Identification and Involvement in Response to Biotic and Abiotic Stresses of lncRNAs in Turbot (Scophthalmus maximus)

Long non-coding RNAs (lncRNAs) play crucial roles in a variety of biological processes, including stress response. However, the number, characteristics and stress-related expression of lncRNAs in turbot are still largely unknown. In this study, a total of 12,999 lncRNAs were identified at the genome-wide level of turbot for the first time using 24 RNA-seq datasets. Sequence characteristic analyses of transcripts showed that lncRNA transcripts were shorter in average length, lower in average GC content and in average expression level as compared to the coding genes. Expression pattern analyses of lncRNAs in 12 distinct tissues showed that lncRNAs, especially lincRNA, exhibited stronger tissue-specific expression than coding genes. Moreover, 612, 1351, 1060, 875, 420 and 1689 differentially expressed (DE) lncRNAs under Vibrio anguillarum, Enteromyxum scophthalmi, and Megalocytivirus infection and heat, oxygen, and salinity stress conditions were identified, respectively. Among them, 151 and 62 lncRNAs showed differential expression under various abiotic and biotic stresses, respectively, and 11 lncRNAs differentially expressed under both abiotic and biotic stresses were selected as comprehensive stress-responsive lncRNA candidates. Furthermore, expression pattern analysis and qPCR validation both verified the comprehensive stress-responsive functions of these 11 lncRNAs. In addition, 497 significantly co-expressed target genes (correlation coefficient (R) > 0.7 and q-value < 0.05) for these 11 comprehensive stress-responsive lncRNA candidates were identified. Finally, GO and KEGG enrichment analyses indicated that these target genes were enriched mainly in molecular function, such as cytokine activity and active transmembrane transporter activity, in biological processes, such as response to stimulus and immune response, and in pathways, such as protein families: signaling and cellular processes, transporters and metabolism. These findings not only provide valuable reference resources for further research on the molecular basis and function of lncRNAs in turbot but also help to accelerate the progress of molecularly selective breeding of stress-resistant turbot strains or varieties.

The antipsychotic drug olanzapine altered lipid metabolism in the common carp (Cyprinus carpio L.): Insight from the gut microbiota-SCFAs-liver axis

Olanzapine (OLA) is a common drug used to treat schizophrenia and has recently come under increasing scrutiny as an emerging contaminant. However, its impact on lipid metabolism in fish and its mechanisms of action are not well understood. In this study, common carp were exposed to 0, 10, 100, and 250 μM OLA for 60 days. The results indicated that OLA exposure increased weight gain, total cholesterol (TC), low-density lipoprotein (LDL), and triglycerides (TG) and decreased high-density lipoprotein (HDL). In addition, lipids accumulated in the liver of the common carp. To explore the underlying mechanisms of action, gut microbiota, short-chain fatty acids (SCFAs), liver transcripts, and genes related to lipid metabolism were measured. It was discovered that OLA exposure altered the common carp gut microbiota composition and increased the abundance of SCFA-producing bacteria. Correspondingly, this study showed that OLA exposure increased the levels of SCFAs, which are highly relevant to the development of lipid accumulation. Transcriptome sequencing results indicated that OLA exposure could change lipid metabolism signalling pathways, including steroid biosynthesis, the PPAR signalling pathway, asglycerophospholipid metabolism, glycerolipid metabolism, and fatty acid metabolic pathways of the common carp. Additionally, OLA exposure interrupted lipid metabolism by means of significant upregulation of lipid synthesis-related genes, including pparγ, srebp1, and fas. OLA exposure also resulted in significant lipolysis-related gene downregulation, including cpt, lpl, hsl, and pparα. The results of this study indicated that contamination of aquatic environments with OLA alters lipid metabolism in common carp. In addition, the underlying mechanism might be due in part to the modulation of the gut microbiota-SCFA-PPAR signalling pathway.

Thermal Stress Induces Metabolic Responses in Juvenile Qingtian Paddy Field Carp Cyprinus carpio var qingtianensis

Extreme fluctuations in water temperature lead to significant economic losses for the aquaculture industry. Cyprinus carpio var qingtianensis (locally called Qingtian paddy field carp), is a local variety commonly found in Zhejiang province, China. Unlike traditional aquaculture environments, the water temperature range between day and night in the rice field environment is much larger, and the high temperature in summer may exceed the growth threshold of fish because there is no manual intervention; therefore, the study of how the Qingtian paddy field carp (PF carp) adapts to high-temperature conditions can shed light how the species adapt to the rice field environment. To investigate the molecular mechanisms of this fish under thermal stress, the liver metabolomics of Qiangtian paddy field carp (PF carp) were analyzed. In this study, metabolomics was used to examine the metabolic reaction of PF carp (102 days old, 104.69 ± 3.08 g in weight, 14.65 ± 0.46 cm in length) at water temperatures of 28 °C (control group, CG), 34 °C (experimental group (EG) 34), and 38 °C (EG38). The results show that 175 expression profile metabolites (DEMs), including 115 upregulated and 60 downregulated metabolites, were found in the CG vs. EG34. A total of 354 DEMs were inspected in CG vs. EG38, with 85 metabolites downregulated and 269 metabolites upregulated. According to the pathway enrichment study, various pathways were altered by thermal stress, including those of lipid, amino-acid, and carbohydrate metabolism. Our study presents a potential metabolic profile for PF carp under thermal stress. It also demonstrates how the host responds to thermal stress on a metabolic and molecular level.

Effects of stocking density on the growth performance, mitophagy, endocytosis and metabolism of Cherax quadricarinatus in integrated rice-crayfish farming systems

Red claw crayfish (Cherax quadricarinatus) is an economic freshwater shrimp with great commercial potential. However, the suitable stocking density of C. quadricarinatus is still unclear in integrated rice-crayfish farming system. Thus, this study aimed to investigate the effects of stocking density on growth performance, mitophagy, endocytosis and metabolism of C. quadricarinatus. The C. quadricarinatus was reared at low density (LD, 35.73 g/m²), middle density (MD, 71.46 g/m²) and high density (HD, 107.19 g/m²) in an integrated rice-crayfish farming system. After 90 days of farming, the growth performance of C. quadricarinatus significantly decreased in the MD and HD groups relative to that in the LD group. The HD treatment caused oxidative stress and lipid peroxidation at the end of the experiment in hepatopancreas. Transcriptome analysis showed that there were 1,531 DEGs (differently expressed genes) between the LD group and HD group, including 1,028 upregulated genes and 503 downregulated genes. KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis indicated that the DEGs were significantly enriched in endocytosis and mitophagy pathways. Meanwhile, four lipid metabolism pathways, including biosynthesis of unsaturated fatty acids, fatty acid biosynthesis, glycerolipid metabolism and glycerophospholipid metabolism, exhibited an upregulated tendency in the HD group. In conclusion, our data showed that when the stocking density reached up to 207.15 g/m² in HD group, the growth performance of C. quadricarinatus was significantly inhibited in this system. Meanwhile, the data indicated that C. quadricarinatus may respond to the stressful condition via activating antioxidant defense system, endocytosis, mitophagy and metabolism-related pathways in hepatopancreas.

Characterization of Gut Microbiome in the Mud Snail Cipangopaludina cathayensis in Response to High-Temperature Stress

Simple Summary

This study investigated the effects of high-temperature stress on the intestinal microbiome of Cipangopaludina cathayensis. High-temperature exposure significantly changed the intestinal microbiota structure of C. cathayensis. The relative abundance of putatively beneficial bacteria decreased, whereas the relative abundance of putatively pathogenic bacteria increased after thermal stress. Consistent with the trends of change in the intestinal microbiota, the high-temperature treatment inhibited some carbohydrate metabolism pathways and induced certain disease-related pathways. Thermal stress disrupts the homeostasis of gut microbiota, which may lead to disease outbreak in C. cathayensis.

Abstract

The mud snail Cipangopaludina cathayensis is a widely distributed species in China. Particularly in Guangxi province, mud snail farming contributes significantly to the economic development. However, global warming in recent decades poses a serious threat to global aquaculture production. The rising water temperature is harmful to aquatic animals. The present study explored the effects of high temperature on the intestinal microbiota of C. cathayensis. Snail intestinal samples were collected from the control and high-temperature groups on days 3 and 7 to determine the gut microbiota composition and diversity. Gut bacterial community composition was investigated using high-throughput sequencing of the V3–V4 region of bacterial 16S rRNA genes. Our results suggested that thermal stress altered the gut microbiome structure of C. cathayensis. At the phylum level, Proteobacteria, Bacteroidetes, and Firmicutes were dominant in C. cathayensis gut microbiota. The T2 treatment (32 ± 1 °C, day 7) significantly decreased the relative abundance of Firmicutes, Actinobacteria, and Deinococcus-Thermus. In T2, the abundance of several genera of putatively beneficial bacteria (Pseudomonas, Aeromonas, Rhodobacter, and Bacteroides) decreased, whereas the abundance of Halomonas—a pathogenic bacterial genus—increased. The functional prediction results indicated that T2 treatment inhibited some carbohydrate metabolism pathways and induced certain disease-related pathways (e.g., those related to systemic lupus erythematosus, Vibrio cholerae infection, hypertrophic cardiomyopathy, and shigellosis). Thus, high temperature profoundly affected the community structure and function of C. cathayensis gut microbiota. The results provide insights into the mechanisms associated with response of C. cathayensis intestinal microbiota to global warming.

Comparison of lipid metabolism between broodstock and hybrid offspring in the hepatopancreas of juvenile shrimp (Macrobrachium nipponense): Response to chronic ammonia stress

Ammonia nitrogen is a major pollutant that causes great physiological harm to crustaceans in culture. In this study, we conducted a 28 day chronic ammonia nitrogen stress experiment with broodstock populations (Dianshan, DS) and hybrid offspring populations (DS ♀ × CD (Changjiang ♂ × Dongting ♀), SCD) exposed to 0, 1 and 10 mg/L of ammonia concentrations. A 28 day feeding trial and chronic ammonia nitrogen stress were used to investigate the effects on the growth performance, histological structure and lipid metabolism of juvenile shrimp, Macrobrachium nipponense. Our results indicated that survival rates in the SCD groups were significantly higher than those in the DS groups, whereas weight and length gain rates were not significantly different between the groups (p > 0.05). Histological structure results showed that the number of vacuoles in the DS group was significantly higher than that in the SCD group and hepatopancreas cell structures were disrupted in the ammonia treatment groups. The results of oil red staining showed that the number of lipid droplets increased significantly with the increase in ammonia concentration. As the ammonia concentration increased, fatty acid contents, lipid enzyme activities and lipid metabolism-related gene expression all tended to rise. In conclusion, ammonia nitrogen exposure caused damage to the hepatopancreas structure of juvenile shrimp and disturbed the lipid metabolism of the hepatopancreas. In addition, the SCD population had stronger stress resistance than the DS population when subjected to the same concentration of ammonia nitrogen stress.