Endoplasmic Reticulum Stress-Related Genes in Yellow Catfish Pelteobagrus fulvidraco: Molecular Characterization, Tissue Expression, and Expression Responses to Dietary Copper Deficiency and Excess

Effects of Stocking Density on the Growth Performance, Physiological Parameters, Antioxidant Status and Lipid Metabolism of Pelteobagrus fulvidraco in the Integrated Rice-Fish Farming System

Pelteobagrus fulvidraco is a freshwater fish commonly raised in rice fields, yet the optimal stocking density for this species remains unknown. Therefore, this study aimed to investigate the appropriate stocking density of P. fulvidraco in integrated rice-fish farming systems. Three different stocking densities--low density (LD, 125 g/m2), middle density (MD, 187.5 g/m2), and high density (HD, 250 g/m2)--were set up to evaluate P. fulvidraco's growth performance, stress indices, immune function, antioxidant status, and lipid metabolism after 90 days of farming. The results indicated that HD treatment had a detrimental effect on P. fulvidraco's growth parameters. HD treatment led to an increase in cortisol (Cor) and lactate (La) levels, but a decrease in glucose (Glu) content in serum. After 90 days of farming, an immune response accompanied by the increase of complement 3 (C3), C4, and immunoglobulin M (IgM) was observed in the HD group. Meanwhile, HD treatment induced oxidative stress and altered antioxidative status evidenced by the levels of catalase (CAT), glutathione peroxidase (Gpx), glutathione (GSH), malondialdehyde (MDA), superoxide dismutase (SOD), and total antioxidant capacity (T-AOC) in serum or liver. Additionally, the lipid metabolism-related genes including lipoprotein lipase (lpl), peroxisome proliferators-activated receptor (pparα), carnitine palmitoyltransferase-1 (cpt-1), and sterol regulatory element binding protein-1 (srebp-1) were markedly downregulated in the HD and/or MD group after 90 days of farming. In conclusion, this study contributes to a better understanding of P. fulvidraco's response to different stocking densities in integrated rice-fish farming systems. We suggest that the appropriate stocking density for P. fulvidraco in these farming systems should be below 250 g/m2, considering both fish growth and physiological responses.

Integration of transcriptome and proteome analyses reveals the regulation mechanisms of Larimichthys polyactis liver exposed to heat stress

Small yellow croaker (Larimichthys polyactis) is one of the most economically important marine fishery species. L. polyactis aquaculture has experienced stress response and the frequent occurrence of diseases, bringing huge losses to the aquaculture industry. Little is known about the regulation mechanism of heat stress response in L. polyactis. In this study, to provide an overview of the heat-tolerance mechanism of L. polyactis, the transcriptome and proteome of the liver of L. polyactis on the 6 h after high temperature (32 °C) treatment were analyzed using Illumina HiSeq 4000 platform and isobaric tag for relative and absolute quantitation (iTRAQ). A total of 3700 upregulated and 1628 downregulated genes (differentially expressed genes, DEGs) were identified after heat stress in L. polyactis. Also, 198 differentially expressed proteins (DEPs), including 117 upregulated and 81 downregulated proteins, were identified. Integrative analysis revealed that 72 genes were significantly differentially expressed at transcriptome and protein levels. Functional analysis showed that arginine biosynthesis, tyrosine metabolism, pentose phosphate pathway, starch and sucrose metabolism, and protein processing in the endoplasmic reticulum were the main pathways responding to heat stress. Among the pathways, protein processing in the endoplasmic reticulum was enriched by most DEGs/DEPs, which suggests that this pathway may play a more important role in the heat stress response. Further insights into the pathway revealed that transcripts and proteins, especially HSPs and PDIs, were differentially expressed in response to heat stress. These findings contribute to existing data describing the fish response to heat stress and provide information about protein levels, which are of great significance to a deeper understanding of the heat stress responding regulation mechanism in L. polyactis and other fish species.

Exposure to copper nanoparticles impairs ion uptake, and acid and ammonia excretion by ionocytes in zebrafish embryos

The potential toxicity of copper nanoparticles (CuNPs) to early stages of fishes is not fully understood, and little is known about their effects on ionocytes and associated functions. This study used zebrafish embryos as a model to investigate the toxic effects of CuNPs on two subtypes of ionocytes. Zebrafish embryos were exposed to 0.1, 1, and 3 mg L^-1 CuNPs for 96 h. After exposure, whole-body Na⁺ and Ca²⁺ contents were significantly reduced at ≥0.1 mg L^-1, while the K⁺ content had decreased at ≥1 mg L^-1. H⁺ and NH₄⁺ excretion by the skin significantly decreased at ≥1 mg L^-1. The number of living ionocytes labeled with rhodamine-123 had significantly decreased with ≥0.1 mg L^-1 CuNPs. The ionocyte subtypes of H⁺-ATPase-rich (HR) and Na⁺/K⁺-ATPase-rich (NaR) cells were labeled by immunostaining and had decreased with ≥1 mg L^-1. Shrinkage of the apical opening of ionocytes was revealed by scanning electronic microscopy. Functional impairment was also reflected by changes in gene expressions, including ion transporters/channels and Ca²⁺-regulatory hormones. This study shows that CuNP exposure can impair two subtypes of ionocytes and their associated functions, including Na⁺/Ca²⁺ uptake and H⁺/NH₄⁺ excretion in zebrafish embryos.

Identification of five genes in endoplasmic reticulum (ER) stress-apoptosis pathways in yellow catfish Pelteobagrus fulvidraco and their transcriptional responses to dietary lipid levels

The activating transcription factor 4 (ATF4), DNA damage-inducible transcript 3 (DDIT3), growth arrest, and DNA damage-inducible protein 34 (GADD34), endoplasmic reticulum oxidoreductin 1α (ERO1α), and tumor necrosis factor receptor associated factor 2 (TRAF2) cDNAs were first characterized from yellow catfish Pelteobagrus fulvidraco. Compared to corresponding genes of mammals, all of these proteins shared similar conserved domains. Their mRNAs were widely expressed in various tissues, but at variable levels. Dietary lipid levels did not significantly influence ATF4 mRNA expression. mRNA expression of DDIT3 and GADD34 was highest for fish fed the low-lipid diets and lowest for fish fed middle-lipid diets. The mRNA levels of ERO1α and TRAF2 declined with increasing dietary lipid levels. For the first time, we characterized the full-length cDNA sequences of ATF4, DDIT3, GADD34, ERO1α, and TRAF2 and determined their tissue expression profiles and transcriptional responses to dietary lipid levels, which would contribute to our exploration into their biological functions, and providing new insights on relations between ER stress and lipid metabolism in fish.

RNA-seq reveals temporal differences in the transcriptome response to acute heat stress in the Atlantic salmon (Salmo salar)

Acute heat stress is common in aquaculture and can affect diverse physiological processes in fish; however, different species of fish have various mechanisms for heat stress adaptation. In this study, we profiled the transcriptome responses of the Atlantic salmon (Salmo salar) to heat stress at 23 °C for 6 or 24 h, compared with that of fish at a normal temperature of 13 °C. The liver was selected as the target tissue for this analysis. A total of 243 and 88 genes were differentially expressed after 6 and 24 h of heat stress, respectively. Of these, only 22 were common to both time points, and most of these common genes were molecular chaperones such as heat shock cognate 71 kDa protein and heat shock protein 90-alpha. Genes such as activating transcription factor 6, calreticulin, protein disulfide isomerase A3, and protein kinase R-like endoplasmic reticulum kinase-eukaryotic initiation factor 2-alpha were only up-regulated after 6 h of heat stress; most of these genes are involved in the endoplasmic reticulum stress pathway. Indeed, endoplasmic reticulum stress was identified at 6 h but not at 24 h, suggesting that stress response plays an important role in the adaptation of Atlantic salmon to acute heat stress. Other up-regulated genes at 6 h were related to the insulin and nucleotide oligomerization domain-like receptor signaling pathways, which directly eliminate misfolded proteins and sustain sugar and lipid homeostasis. At 24 h, heat stress influenced the expression of steroid and terpenoid backbone biosynthesis, which may influence the sexual development and differentiation of Atlantic salmon. Overall, our results elucidate the transcriptome mechanisms that contribute to short-term heat tolerance in the liver of Atlantic salmon.

CREB element is essential for unfolded protein response (UPR) mediating the Cu-induced changes of hepatic lipogenic metabolism in Chinese yellow catfish (Pelteobagrus fulvidraco)

The present study was conducted to explore the underlying mechanism of unfolded protein response (UPR) mediating the Cu-induced changes of hepatic lipogenic metabolism in a low vertebrate, freshwater teleost yellow catfish Pelteobagrus fulvidraco. To this end, three experiments were conducted. In Exp. 1, we cloned the regions of grp78, perk, ire-1α and atf-6α promoters, and found that multiple cAMP-response element binding protein (CREB) binding sites were identified in their promoter regions. Furthermore, these CREB binding sites played crucial role in transcriptional regulation of UPR. In Exp. 2, the involvement of perk, ire-1α and atf-6α in Cu-induced changes of hepatic lipid metabolism was confirmed by specific miRNA. In Exp. 3, the regulatory mechanism of CREB underlying UPR mediating Cu-induced hepatic lipogenic metabolism were investigated. Cu induced UPR via the activation of CREB binding sites in the promoter regions of grp78, perk, ire-1α and atf-6α. In addition, the inhibition of CREB markedly attenuated the Cu-induced up-regulation of hepatic lipogenic metabolism in hepatocytes. This conclusion was further supported by the results from the trial of CREB over-expression. Taken together, the present study indicated that CREB was essential for UPR mediating Cu-induced lipogenic metabolism, supporting a mechanistic link among CREB, UPR and Cu-induced changes of lipid metabolism.

Identification of eight copper (Cu) uptake related genes from yellow catfish Pelteobagrus fulvidraco, and their tissue expression and transcriptional responses to dietborne Cu exposure

The present working hypothesis is that absorption of dietary Cu is related to mRNA expressions of genes involved in Cu uptake and transport of the intestine in fish. To this end, the full-length cDNA sequences of eight Cu uptake related genes, including two isoforms of copper transporter genes (ctr1 and ctr2), three copper chaperone genes (atox1, ccs and cox17), two Cu-ATPase genes (atp7a and atp7b) and divalent metal ion transporter 1 (dmt1), were cloned and characterized in yellow catfish P. fulvidraco, respectively. Their mRNA tissue expression and transcriptional responses to dietborne Cu exposure were investigated. Compared to the corresponding members of mammals, all of these members in P. fulvidraco shared the similar conserved domain structures. Their mRNAs were expressed in a wide range of tissues (including liver, muscle, spleen, brain, gill, intestine, heart and kidney), but at variable levels. In anterior intestine, mRNA levels of ctr1, cox17, dmt1 and atp7a declined with increasing dietary Cu levels. The mRNA levels of ctr2 and mt were the highest for excess dietary Cu group and showed no significant differences between other two treatments. Atox1 mRNA levels were the highest for Cu-deficient group and showed no significant differences between other two treatments. The mRNA levels of ccs were the highest for Cu-deficient group, followed by Cu-excess group and the lowest for adequate-Cu group. In contrast, atp7b mRNA levels were the highest for Cu-excess group and the lowest for adequate Cu group. In the mid-intestine, mRNA levels of ctr1, ctr2, atox1, ccs, cox17, dmt1 and atp7a declined with increasing dietary Cu levels. Atp7b mRNA levels were the lowest for adequate Cu group and showed no significant differences between other two treatments. Mt mRNA levels were the lowest for adequate Cu group and highest for Cu-excess group. For the first time, our study cloned and characterized ctr1, ctr2, atox1, ccs, cox17, atp7a, atp7b and dmt1 genes in P. fulvidraco and determined their tissue-specific expression, and transcriptional responses in the anterior and mid-intestine of yellow catfish under dietborne Cu exposure, which shed new light on the Cu uptake system and help to understand the molecular mechanisms of Cu homeostasis in fish.

Hepatic transcriptional responses to copper in the three-spined stickleback are affected by their pollution exposure history

Some fish populations inhabiting contaminated environments show evidence of increased chemical tolerance, however the mechanisms contributing to this tolerance, and whether this is heritable, are poorly understood. We investigated the responses of two populations of wild three-spined stickleback (Gasterosteus aculeatus) with different histories of contaminant exposure to an oestrogen and copper, two widespread aquatic pollutants. Male stickleback originating from two sites, the River Aire, with a history of complex pollution discharges, and Siblyback Lake, with a history of metal contamination, were depurated and then exposed to copper (46μg/L) and the synthetic oestrogen ethinyloestradiol (22ng/L). The hepatic transcriptomic response was compared between the two populations and to a reference population with no known history of exposure (Houghton Springs, Dorset). Gene responses included those typical for both copper and oestrogen, with no discernable difference in response to oestrogen between populations. There was, however, some difference in the magnitude of response to copper between populations. Siblyback fish showed an elevated baseline transcription of genes encoding metallothioneins and a lower level of metallothionein induction following copper exposure, compared to those from the River Aire. Similarly, a further experiment with an F1 generation of Siblyback fish bred in the laboratory found evidence for elevated transcription of genes encoding metallothioneins in unexposed fish, together with an altered transcriptional response to 125μg/L copper, compared with F1 fish originating from the clean reference population exposed to the same copper concentration. These data suggest that the stickleback from Siblyback Lake have a differential response to copper, which is inherited by the F1 generation in laboratory conditions, and for which the underlying mechanism may include an elevation of baseline transcription of genes encoding metallothioneins. The genetic and/or epigenetic mechanisms contributing to this inherited alteration of metallothionein transcription have yet to be established.

Endoplasmic reticulum stress and dysregulation of calcium homeostasis mediate Cu-induced alteration in hepatic lipid metabolism of javelin goby Synechogobius hasta

The present study was conducted to investigate the effect of Cu exposure on endoplasmic reticulum (ER) stress and Ca(2+) homeostasis, and also explore the underlying mechanism of the ER stress and Ca(2+) homeostasis in the Cu-induced change of hepatic lipid metabolism in javelin goby Synechogobius hasta. To this end, four experiments were conducted. In experiment 1, the full-length cDNA sequences of two ER molecular chaperones [glucose-regulated protein 78 (GRP78) and calreticulin (CRT)] and three ER stress sensors [PKR-like ER kinase (PERK), inositol requiring enzyme (IRE)-1α, and activating transcription factor (ATF)-6α] cDNAs were firstly characterized from S. hasta. The predicted amino acid sequences for the S. hasta GRP78, CRT, PERK, IRE-1α and ATF-6α revealed that the proteins contained all of the structural features characteristic in other species. mRNAs of the five genes were expressed in various tissues, but their mRNA levels varied among tissues. In experiment 2, S. hasta were exposed to four waterborne Cu concentrations (control, 19μg/l, 38μg/l, and 57μg/l, respectively) for 60days. Cu exposure evoked ER stress in liver of S. hasta in a time- and concentration-course change. In experiment 3, specific inhibitors, 2-aminoethyldiphenyl borate (2-APB) and dantrolene, were used to explore whether Ca(2+) release from ER was involved in the Cu-induced ER stress change. Dantrolene and 2-APB prevented Cu-induced intracellular Ca(2+) elevation, which demonstrated the release of Ca(2+) from the ER was mediated by both RyR and IP3R. In experiment 4, a chemical chaperone, 4-phenyl butyric acid (4-PBA), was used to demonstrate whether Cu-induced alteration in lipid metabolism was suppressed through the attenuation of ER stress. Cu exposure evoked ER stress and sterol-regulator element-binding protein-1c (SREBP-1c) activation in hepatocytes of S. hasta, resulting in dysregulation of hepatic lipid metabolism. 4-PBA attenuated the Cu-induced elevation of mRNA expression of ER stress-related genes. For the first time, our study cloned GRP78, CRT, PERK, IRE-1α and ATF-6α genes in S. hasta and demonstrated their differential expression among tissues. Moreover, the study demonstrated the molecular mechanism by which ER stress might underlie the change of lipid metabolism induced by Cu in S. hasta.