Molecular cloning and differential expression patterns of copper/zinc superoxide dismutase and manganese superoxide dismutase in Hypophthalmichthys molitrix

Transcriptional regulation of the Japanese flounder Cu,Zn-SOD (Jfsod1) gene in RAW264.7 cells during oxidative stress caused by causative bacteria of edwardsiellosis

Edwardsiellosis is one of the most important bacterial diseases in fish, sometimes causing extensive economic losses in the aquaculture industry. Our previous studies demonstrated that the Cu,Zn-SOD (sod1) activity has significantly increased in Japanese flounder, Paralichthys olivaceus, hepatopancreas infected by causative bacteria of edwardsiellosis Edwardsiella tarda NUF251. In this study, NUF251 stimulated intracellular superoxide radical production in mouse macrophage RAW264.7 cells, which was reduced by N-acetylcysteine. This result suggests that NUF251 infection causes oxidative stress. To evaluate the regulatory mechanism of Jfsod1 at transcriptional levels under oxidative stress induced by NUF251 infection, we cloned and determined the nucleotide sequence (1124 bp) of the 5'-flanking region of the Jfsod1 gene. The sequence analysis demonstrated that the binding sites for the transcription factors C/EBPα and NF-IL6 involved in the transcriptional regulation of the mammalian sod1 gene existed. We constructed a luciferase reporter system with the 5'-flanking region (-1124/-1) of the Jfsod1 gene, and a highly increased transcriptional activity of the region was observed in NUF251-infected RAW264.7 cells. Further studies using several mutants indicated that deletion of the recognition region of NF-IL6 (-272/-132) resulted in a significant decrease in the transcriptional activity of the Jfsod1 gene in NUF251-infected RAW264.7 cells. In particular, the binding site (-202/-194) for NF-IL6 might play a major role in upregulating the transcriptional activity of the 5'-flanking region of the Jfsod1 gene in response to oxidative stress induced by NUF251 infection. These results could be provided a new insight to understand the pathogenic mechanism of causative bacteria of edwardsiellosis.

Antioxidant Defence in Labeo rohita to Biotic and Abiotic Stress: Insight from mRNA Expression, Molecular Characterization and Recombinant Protein-Based ELISA of Catalase, Glutathione Peroxidase, CuZn Superoxide Dismutase, and Glutathione S-Transferase

Fish possess numerous enzymatic antioxidant systems as part of their innate immunity. These systems have been poorly studied in Labeo rohita (rohu). The present study characterized and investigated the role of antioxidant genes in the defence mechanisms against two types of stressors, including infection and ammonia stress. Four key genes associated with antioxidant activity-catalase, glutathione peroxidase, glutathione S-transferase, and CuZn superoxide dismutase were successfully cloned and sequenced. These genes were found to be expressed in different tissues and developmental stages of rohu. The expression levels of these antioxidant genes in the liver and anterior kidney tissues of rohu juveniles were modulated in response to bacterial infection (Aeromonas hydrophila), parasite infection (Argulus siamensis), poly I:C stimulation and ammonia stress. Additionally, the recombinant proteins derived from these genes exhibited significant antioxidant and antibacterial activities. These proteins also demonstrated a protective effect against A. hydrophila infection in rohu and had an immunomodulatory role. Furthermore, indirect ELISA assay systems were developed to measure these protein levels in healthy as well as A. hydrophila and ammonia-induced rohu serum. Overall, this study characterized and emphasised the importance of the antioxidant mechanism in rohu's defence against oxidative damage and microbial diseases.

Integrated transcriptome and miRNA sequencing analyses reveal that hypoxia stress induces immune and metabolic disorders in gill of genetically improved farmed tilapia (GIFT, Oreochromis niloticus)

The survival and growth of fish are significantly impacted by a hypoxic environment (low dissolved oxygen). In this study, we compared tissue structure, physiological changes, and mRNA/miRNA transcriptome, in gills of genetically improved farmed tilapia (GIFT, Oreochromis niloticus) between the hypoxic group (DO: 0.55 mg/L, HG) and the control group (DO: 5 mg/L, CG). The results showed that the gill filaments in the hypoxic group showed curling, engorgement, and apoptotic cells increased, and that exposure for 96 h resulted in a reduction in the antioxidant capacity. We constructed and sequenced miRNA and mRNA libraries from gill tissues of GIFT at 96 h of hypoxia stress. Between the HG and CG, a total of 14 differentially expressed (DE) miRNAs and 1557 DE genes were obtained. GO and KEGG enrichment showed that DE genes were mainly enriched in immune and metabolic pathways such as natural killer cell mediated cytotoxicity, steroid biosynthesis, primary immunodeficiency, and synthesis and degradation of ketone bodies. Based on the results of mRNA sequencing and screening for miRNA-mRNA pairs, we selected and verified six DE miRNAs and their probable target genes. The sequencing results were consistent with the qRT-PCR validation results. The result showed that under hypoxia stress, the innate immune response was up-regulated, and the adaptive immune response was down-regulated in the gill of GIFT. The synthesis of cholesterol in gill cells is reduced, which is conducive to the absorption of solvent oxygen. These findings offer fresh information about the processes of fish adaptation to hypoxic stress.

Comparative transcriptome analysis provides novel insights into the molecular mechanism of the silver carp (Hypophthalmichthys molitrix) brain in response to hypoxia stress

The brain of fish plays an important role in regulating growth and adapting to environmental changes. However, few studies have been performed to address the changes in gene expression profiles in fish brains under hypoxic stress. In the present study, silver carp (Hypophthalmichthys molitrix) were kept under hypoxic experimental conditions by using the method of natural oxygen consumption, which resulted in a significant decrease in malondialdehyde (MDA) and glutathione (GSH) content and superoxide dismutase (SOD) activity in the brain. In addition, RNA sequencing (RNA-Seq) was performed to analyze transcriptional regulation in the brains of silver carp under normoxia (control group), hypoxia, semi-asphyxia, and asphyxia conditions. The results of KEGG enrichment pathway analysis showed that the immune system, such as antigen processing and presentation, natural killer cell-mediated cytotoxicity, was enriched in the hypoxia group; the nervous system (e.g., "glutamatergic synapse"), signal transduction (e.g., "calcium signaling pathway"; "foxo signaling pathway"), and signaling molecules and interactions (e.g., "neuroactive ligand-receptor interaction") were enriched in the semi-asphyxia group; and signaling molecules and interactions (e.g., "neuroactive ligand-receptor interaction") were enriched in the asphyxia group. These results provide novel insights into the molecular regulatory mechanism of the fish brain coping with hypoxia stress.

Cu/Zn Superoxide Dismutase and Catalase of Yangtze Sturgeon, Acipenser dabryanus: Molecular Cloning, Tissue Distribution and Response to Fasting and Refeeding

Superoxide dismutase and catalase are two major antioxidant enzymes in the fish antioxidant defense system, which can remove excess reactive oxygen species and protect fish from stress-induced oxidative damage. The present study aimed to clone the sequences of Yangtze sturgeon, Acipenser dabryanus, Cu/Zn superoxide dismutase (AdCu/Zn-SOD) and catalase (AdCAT), and to explore changes of gene expression in the liver and intestine during fasting and refeeding. A total of 120 fish were exposed to four fasting and refeeding protocols (fasting for 0, 3, 7, or 14 d and then refeeding for 14 d). The coding sequences of AdCu/Zn-SOD and AdCAT encoded 155 and 526 amino acid proteins, respectively, both of which were expressed mainly in the liver. During fasting, when compared to the control group, liver AdCu/Zn-SOD expression was significantly higher in the 3- and 14-d groups, whereas its intestinal expression increased significantly only in the 7-d group. Liver AdCAT expression increased significantly in the 3-, 7-, and 14-d groups. During refeeding, liver AdCu/Zn-SOD expression increased significantly in the 3-, 7-, and 14-d groups compared with those in the control group. Similarly, intestinal AdCu/Zn-SOD expression increased significantly in the 3- and 7-d groups. Moreover, intestinal AdCAT expression was significantly higher in the 3-d group than in the control group, but decreased significantly in the 14-d group. Our findings indicated that AdCu/Zn-SOD and AdCAT play important roles in protecting fish against starvation-induced oxidative stress. Yangtze sturgeon exhibited the potential to adapt to a starvation and refeeding regime.

A copper-zinc-superoxide dismutase (CuZnSOD) from redlip mullet, Liza haematocheila: Insights to its structural characteristics, immune responses, antioxidant activity, and potent antibacterial properties

Copper-zinc superoxide dismutase (CuZnSOD) is a nuclear-encoded metalloenzyme responsible for scavenging harmful reactive oxygen species (ROS). In this study, the CuZnSOD homolog from redlip mullet (Liza haematochelia) (MuCuZnSOD) was structurally and functionally characterized to evaluate its antioxidant capacity, antibacterial properties, and protective level in various pathogenic stress conditions. Structural characteristics of MuCuZnSOD were evaluated using different bioinformatics tools. Pairwise sequence comparison and evolutionary tree structure revealed that the MuCuZnSOD sequence was closely related to the CuZnSOD sequence of Oplegnathus fasciatus with a 94.2% sequence identity. Sequence alignment analysis indicated that the CuZnSOD domain was well conserved. The highest transcriptional expression of MuCuZnSOD was identified in the blood. Immune challenge with lipopolysaccharide (LPS), Lactococcus garvieae, and polyinosinic-polycytidylic acid (poly I:C) exhibited an increased MuCuZnSOD mRNA expression in the blood and liver. Transfected green fluorescent protein-fused MuCuZnSOD was localized in the cytoplasm. Recombinant MuCuZnSOD (rMuCuZnSOD) was overexpressed in a bacterial system. The rMuCuZnSOD possessed significant antioxidant properties as determined by conventional xanthine oxidase assay. The optimum pH and temperature of rMuCuZnSOD were found to be pH 9 and 25 °C, respectively. rMuCuZnSOD enzyme activity increased in a concentration-dependent manner. Treatment with potassium cyanide highly inhibited the rMuCuZnSOD activity. rMuCuZnSOD possessed a significant peroxidation activity in the presence of HCO₃- ions as demonstrated by the increased viability in cells treated with the enzyme in the presence of hydrogen peroxide. Antibacterial assays showed that rMuCuZnSOD had significant growth-inhibitory effects on both gram-positive and gram-negative bacteria. Collectively, our findings demonstrate that MuCuZnSOD is an essential antioxidant protein, which regulates the host defense mechanisms and innate immunity under oxidative stress.

Cloning of Mn-SOD gene and its mRNA expression difference and antioxidant enzyme activities under hypoxia stress of cobia Rachycentron canadum

BACKGROUND

Environmental hypoxia affects the survival and development of organisms. It is also an important environmental factor that leads to oxidative damage. Hypoxia is a condition in which tissues are deprived of oxygen; reoxygenation is the phenomenon in which hypoxic tissues are exposed to oxygen. Hypoxia-reoxygenation is vital in pathogenesis, where the production of reactive oxygen species and antioxidant disparity significantly contribute to disease progression, and it is one of the most common physiological stressors in the aquaculture industry.

METHODS AND RESULTS

In this study, the full length of complementary DNA (cDNA) of the manganese superoxide dismutase (Mn-SOD) gene of healthy cobia Rachycentron canadum was analysed using rapid amplification of cDNA ends. The real-time quantitative Polymerase Chain Reaction was used to measure the expression levels of Mn-SOD mRNAs in various tissues (heart, muscle, brain, liver, kidney, gill, intestine, and spleen). The 2^-ΔΔCT method was used to performed the expression analysis. The experimental data were analysed using SPSS ver. 19.0 ( https://spss.software.informer.com/19.0/ ). P < 0.05 and P < 0.01 were set as significant differences. The values were articulated as mean ± standard deviation. The Mn-SOD gene cDNA sequence was 1209 bp long, including a 684 bp open reading frame, 42 bp 5'UTR and 483 bp 3'UTR, encoding 227 amino acids. Under hypoxia-reoxygen stress, the expression of Mn-SOD in brain tissue was significantly lower than in the control group after 8 h of reoxygenation and higher than the control group after 24 h. Hypoxia and subsequent reoxygenation triggered a disturbance in antioxidant homeostasis, displayed in the modification of GPx expression/activity in the liver: GPx was improved.

CONCLUSIONS

These results provide valuable information on the role of Mn-SOD regulation in oxidative stress caused by hypoxia.

Superoxide Dismutase Multigene Family from a Primitive Chondrostean Sturgeon, Acipenser baerii: Molecular Characterization, Evolution, and Antioxidant Defense during Development and Pathogen Infection

Three distinct superoxide dismutases (SODs)-copper/zinc-SOD (SOD1), manganese-SOD (SOD2), and extracellular copper/zinc-SOD (SOD3)-were identified from a primitive chondrostean fish, Acipenser baerii, enabling the comparison of their transcriptional regulation patterns during development, prelarval ontogeny, and immune stimulation. Each A. baerii SOD isoform (AbSOD) shared conserved structural features with its vertebrate orthologs; however, phylogenetic analyses hypothesized a different evolutionary history for AbSOD3 relative to AbSOD1 and AbSOD2 in the vertebrate lineage. The AbSOD isoforms showed different tissue distribution patterns; AbSOD1 was predominantly expressed in most tissues. The expression of the AbSOD isoforms showed isoform-dependent dynamic modulation according to embryonic development and prelarval ontogenic behaviors. Prelarval microinjections revealed that lipopolysaccharide only induced AbSOD3 expression, while Aeromonas hydrophila induced the expression of AbSOD2 and AbSOD3. In fingerlings, the transcriptional response of each AbSOD isoform to bacterial infection was highly tissue-specific, and the three isoforms exhibited different response patterns within a given tissue type; AbSOD3 was induced the most sensitively, and its induction was the most pronounced in the kidneys and skin. Collectively, these findings suggest isoform-dependent roles for the multigene SOD family in antioxidant defenses against the oxidative stress associated with development and immune responses in these endangered sturgeon fish.

miR-489-3p Regulates the Oxidative Stress Response in the Liver and Gill Tissues of Hybrid Yellow Catfish (Pelteobagrus fulvidraco♀ × P. vachelli♂) Under Cu2+ Exposure by Targeting Cu/Zn-SOD

Copper/zinc superoxide dismutase (Cu/Zn-SOD) plays critical roles in protecting cells and tissues against oxidative damage. Excessive copper ions (Cu2+) in water can damage the cells of aquatic organisms, leading to impaired growth and development and reduced antioxidant defenses. Many regulatory factors control the response to excess Cu2+. Among them, microRNAs (miRNAs) are important small RNAs that regulate the expression of their target genes and participate in the oxidative stress response. In the present study, we used bioinformatics and dual luciferase reporter gene analyses to demonstrate that the miR-489-3p of hybrid yellow catfish (Pelteobagrus fulvidraco♀ × P. vachelli♂) binds to the 3'-untranslated region (UTR) of its target gene, which encodes a Cu/Zn-SOD. The regulatory relationship between this miRNA and its target gene Cu/Zn-SOD was analyzed using qRT-PCR and luciferase activity assays. We also investigated the effect of the loss of miR-489-3p expression on the oxidative stress response of hybrid yellow catfish exposed to Cu2+. The Cu/Zn-SOD 3'UTR region was found to be fully complementary to positions 2-9 of the 5'-end seed region of miR-489-3p. The miR-489-3p expression levels were negatively related to Cu/Zn-SOD expression. Silencing of miR-489-3p up-regulated Cu/Zn-SOD expression in the liver and gill tissues, increased activities of SOD and catalase, and reduced the malondialdehyde content. This study is the first to demonstrate that miR-489-3p targets Cu/Zn-SOD to mediate the oxidative response to metal stress. These findings provide a theoretical basis for further studies on the response to oxidative stress caused by metals in cultured fish, and provide an experimental basis for the management of the culture environment.

Molecular characterization of manganese superoxide dismutase (MnSOD) from sterlet Acipenser ruthenus and its responses to Aeromonas hydrophila challenge and hypoxia stress

A novel gene encoding the mitochondrial manganese superoxide dismutase from sterlet Acipenser ruthenus (Ar-MnSOD) was cloned. The full-length cDNA of MnSOD was of 1040 bp with a 672 bp open reading frame encoding 224 amino acids and the deduced amino acid sequence was located in mitochondria. Sequence comparison analysis showed that Ar-MnSOD was highly similar to MnSODs of invertebrates and vertebrates, especially those of freshwater Cyprinidae fishes and mammals. Phylogenetic analysis revealed that Ar-MnSOD was distant from MnSODs of other fishes and belonged to the family of mitochondrial MnSODs (mMnSOD). Consistently, Ar-MnSOD was located in mitochondria. The 3D structure of Ar-MnSOD was predicted and the overall structure was similar to that of MnSODs of humans and the bay scallop Argopecten irradians. In addition, mRNA of Ar-MnSOD was detected to extensively express in all tissues, with the highest level in brain and liver. Spleen and head kidney inoculation of Aeromonas hydrophila led to a significant up-regulation of Ar-MnSOD transcript levels. Also, hypoxia induced a transient increase in transcription of Ar-MnSOD in the gills, but not in the heart and brain, suggesting metabolic depression in these vital organs. The results also implied the anti-hypoxia properties of Ar-MnSOD in the related tissues and proved that Ar-MnSOD was involved in the stress response and (anti) oxidative processes triggered by hypoxia. The results indicated that Ar-MnSOD is induced upon A. hydrophila infection and hypoxia, consistent with its role in host immune and stress-induced anti-oxidative responses.

The molecular characterizations of Cu/ZnSOD and MnSOD and its responses of mRNA expression and enzyme activity to Aeromonas hydrophila or lipopolysaccharide challenge in Qihe crucian carp Carassius auratus

Superoxide dismutases (SODs), as the prime antioxidant enzymes, present the first line of defense against oxidative stress caused by excessive reactive oxygen species (ROS) in organism. In the study, two distinct members of SOD family were cloned and analyzed in Qihe crucian carp Carassius auratus (designated as CaCu/ZnSOD and CaMnSOD, respectively). The full-length cDNA of CaCu/ZnSOD is 759 bp, containing a 5' -untranslated region (UTR) of 39 bp, a ORF (including stop codon, TAG) of 465 bp and a 3'-UTR of 255 bp. The ORF of CaCu/ZnSOD encodes a protein of 154 amino acids (aa), in which, two Cu/ZnSOD signature (⁴⁵GFHVHAFGDNT⁵⁵ and ¹³⁹GNAGGRLACGVI¹⁵⁰) and four conserved amino acids for Cu/Zn²⁺-binding sites (H64, H72, H81 and D84) were observed. The full-length CaMnSOD cDNA (960 bp) consists of a 5'-UTR of 114 bp, a ORF of 675 bp and a 3'-UTR of 231 bp, the ORF of CaMnSOD encodes a 224 aa protein with a 26 aa mitochondrial-targeting sequence (MTS) in the N-terminus, and four conserved amino acids for manganese binding (H52, H100, D185 and H189) were observed. Multiple alignment and the structural analysis revealed two Cu/ZnSOD signature motifs and a MnSOD signature motif as well as the invariant binding sites for Cu²⁺/Zn²⁺ in CaCu/ZnSOD and Mn²⁺ in CaMnSOD. The phylogenetic analysis indicated that CaCu/ZnSOD was homologous to cytosolic Cu/ZnSODs, and CaMnSOD was high similarity with mitochondrial MnSODs from other fish. The tissue distribution analysis demonstrated that CaCu/ZnSOD and CaMnSOD were highly expressed in liver, heart and muscle. The dynamic expressions of CaCu/ZnSOD and CaMnSOD were observed after the challenges with Aeromonas hydrophila or LPS, which generally increased in liver, gill, kidney and spleen, while, the mRNA expressions were down-regulated at some time points in head kidney. The enzyme activities increased after A. hydrophila or LPS challenge, compared to the control. In this study, the molecular structures and functional motifs of CaCu/ZnSOD and CaMnSOD were determined, and it is crucial for us to understand the biological functions of SODs. The highest level in liver showed that the function of liver to remove ROS is much more important. The obvious responses of mRNA expression levels and enzyme activities to pathogens indicate the important roles of CaCu/ZnSOD and CaMnSOD in antioxidant defense in C. auratus.

Characterization of basic immune function parameters in the fathead minnow (Pimephales promelas), a common model in environmental toxicity testing

The fathead minnow (Pimephales promelas) is an environmental sentinel species, commonly used in toxicity testing. However, there is a lack of data regarding basic immune function in this species. To improve the usefulness of the fathead minnow as a model for basic immune function and immunotoxicity, this study sought to 1) compare the differential expression of immune function genes in naïve fathead minnows and 2) determine the effects of pathogen exposure on immune gene expression and spleen index. To accomplish this, kidney, spleen and liver tissue were collected three days post injection (dpi) from adult male fathead minnows from each of the following groups: 1) uninjected control 2) sham-injected (Hank's balanced salt solution) and 3) pathogen-injected (Yersinia ruckeri). Spleen tissue was also collected at seven and 14 dpi. Differential tissue expression of immune function genes was evaluated in naïve minnows and expression patterns were similar to those found in other fish species, with liver tissue generally having the highest amount of expression. Following pathogen injection, the expression of complement component 3 (c3) (4.4-fold, kidney; 2.5-fold, liver), interleukin 11 (il11) (4.8-fold, kidney; 15.2-fold, liver) and interleukin 1β (il1β) (8.2-fold, kidney; 17.2-fold, spleen; 2.6-fold, liver) were significantly upregulated. Elastase 2 (elas2) was significantly downregulated (5.8-fold) in liver tissue. A significant increase in spleen index at seven dpi was also observed in pathogen-injected minnows. This study has identified endpoints that are part of the normal response to pathogen in fathead minnows, an essential step toward the development of the fathead minnow as a model for immunotoxicity evaluations.

Copper-zinc-superoxide dismutase (CuZnSOD), an antioxidant gene from seahorse (Hippocampus abdominalis); molecular cloning, sequence characterization, antioxidant activity and potential peroxidation function of its recombinant protein

Copper-zinc-superoxide dismutase (CuZnSOD) from Hippocampus abdominalis (HaCuZnSOD) is a metalloenzyme which belongs to the ubiquitous family of SODs. Here, we determined the characteristic structural features of HaCuZnSOD, analyzed its evolutionary relationships, and identified its potential immune responses and biological functions in relation to antioxidant defense mechanisms in the seahorse. The gene had a 5' untranslated region (UTR) of 67 bp, a coding sequence of 465 bp and a 3' UTR of 313 bp. The putative peptide consists of 154 amino acids. HaCuZnSOD had a predicted molecular mass of 15.94 kDa and a theoretical pI value of 5.73, which is favorable for copper binding activity. In silico analysis revealed that HaCuZnSOD had a prominent Cu-Zn_superoxide_dismutase domain, two Cu/Zn signature sequences, a putative N-glycosylation site, and several active sites including Cu(2+) and Zn(2+) binding sites. The three dimensional structure indicated a β-sheet barrel with 8 β-sheets and two short α-helical regions. Multiple alignment analyses revealed many conserved regions and active sites among its orthologs. The highest amino acid identity to HaCuZnSOD was found in Siniperca chuatsi (87.4%), while Maylandia zebra shared a close relationship in the phylogenetic analysis. Functional assays were performed to assess the antioxidant, biophysical and biochemical properties of overexpressed recombinant (r) HaCuZnSOD. A xanthine/XOD assay gave optimum results at pH 9 and 25 °C indicating these may be the best conditions for its antioxidant action in the seahorse. An MTT assay and flow cytometry confirmed that rHaCuZnSOD showed peroxidase activity in the presence of HCO3(-). In all the functional assays, the level of antioxidant activity of rHaCuZnSOD was concentration dependent; metal ion supplementation also increased its activity. The highest mRNA expressional level of HaCuZnSOD was found in blood. Temporal assessment under pathological stress showed a delay response by HaCuZnSOD. Our findings demonstrated that HaCuZnSOD is an important antioxidant, which might be involved in the host antioxidant defense mechanism against oxidative stress.

Effects of salinity change on two superoxide dismutases (SODs) in juvenile marbled eel Anguilla marmorata

Salinity is one of the most important factors that affect the fish growth and survival. Superoxide dismutases (SODs), as the primary antioxidant enzymes, play a first role in the process of preventing oxidative stress caused by excessive superoxide anion (O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${}_{2}^{-}$\end{document}2−) in living organisms. In the present study, we investigated the effects of salinity on the gene expressions as well as enzymatic activities of MnSOD and Cu/ZnSOD in gill, intestine, kidney, liver and muscle tissues of the marbled eel Anguilla marmorata. We found that the liver might possess stronger redox capacity compared with other tissues. Furthermore, the gene expressions and enzymatic activities of SODs in juvenile marbled eels could be effectively enhanced by low salinity but inhibited when the salinity was higher than the body tolerance. Our findings indicated that MnSOD and Cu/ZnSOD played vital roles in the adaptation of marbled eels to salinity variation, which contributed to the elucidation of physiological adaptation and regulatory mechanism of SODs in eels.

Modulated expression and enzymatic activities of Darkbarbel catfish, Pelteobagrus vachelli for oxidative stress induced by acute hypoxia and reoxygenation

Large changes in oxygen availability in aquatic environments, ranging from anoxia through to hyperoxia, can lead to corresponding wide variation in the production of reactive oxygen species (ROS) by fish with aquatic respiration. In order to evaluate the effects of hypoxia and reoxygenation on oxidative stress in fish, the mRNA and protein expression of SODs (Cu/Zn-SOD and Mn-SOD) as well as indices (CP, LPO and MDA) and enzymatic activities (SOD, CAT, GPx, GR and GST) were analyzed in liver and brain tissues of Pelteobagrus vachelli. Predominant expression of PvSOD2 was detected in heart, brain, and liver. In contrast, PvSOD1 was highly expressed in liver. Based on the expression patterns of above parameters, we inferred that brain tissue of P. vachelli under 0.7 mg/L degree of acute hypoxia condition could experience hypometabolic states or no suffering stress, but brain tissue has effective mechanisms to minimize or prevent oxidative stress during the transition from hypoxia to reoxygenation. Our results also demonstrated an increased expression of SODs and enzymatic activities for oxidative stress in liver under hypoxic conditions, which supports the hypothesis that anticipatory preparation takes place in order to deal with the encountered oxidative stress during the recovery from hypoxia as proposed by M. Hermes-Lima. Therefore, this study will provide a clue to better understand the action mode of antioxidant genes and enzymes under oxidative stress in fish.

A manganese superoxide dismutase (MnSOD) from ark shell, Scapharca broughtonii: Molecular characterization, expression and immune activity analysis

Manganese superoxide dismutase (MnSOD) is one of the key members of the antioxidant defense enzyme family, however, data regarding to the immune function of MnSOD in mollusks still remain limited now. In this study, a full-length MnSOD cDNA was identified by rapid amplification of cDNA ends (RACE) method from cDNA library of ark shell Scapharca broughtonii (termed SbMnSOD). The cDNA contained an open reading frame (ORF) of 696 bp which encoded a polypeptide of 232 amino acids, a 5'-UTR with length of 32 bp and a 3'-UTR of 275 bp. Four putative amino acid residues (His-57, His-105, Asp-190 and His-194) responsible for manganese coordination were located in the most highly conserved regions of SbMnSOD and the signature sequence (DVWEHAYY) also existed in SbMnSOD. The deduced amino acid sequence of SbMnSOD shared high homology to MnSOD from other species. All those data revealed that the SbMnSOD was a novel member of the MnSOD family. The mRNA expression profiles of SbMnSOD in tissues of foot, gill, mantle, adductor muscle, hemocytes and hepatopancreas analyzed by quantitative real-time PCR (qRT-PCR) suggested the mRNA transcripts of SbMnSOD distributed in all the examined tissues. Importantly, Vibrio anguillarum challenge resulted in the increased expression of SbMnSOD mRNA with a regular change trend in all examined tissues, indicating SbMnSOD actively participated in the immune response process. What's more, further analysis on the antibacterial activity of the recombinant SbMnSOD showed that the fusion protein could remarkably inhibit growth of both Gram-positive and Gram-negative bacteria. The present results clearly suggested that SbMnSOD was an acute phase protein involved in the immune reaction in S. broughtonii.

Molecular cloning, tissue distribution and expression analysis of a manganese superoxide dismutase in blunt snout bream Megalobrama amblycephala

The full-length mitochondrial manganese superoxide dismutase cDNA of blunt snout bream Megalobrama amblycephala (denoted as MamMnSOD) was identified in liver using homology cloning and rapid amplification of cDNA ends. The full-length cDNA of MamMnSOD consisted of 986 bp, with an open reading frame encoding 224 amino acids, a 58-bp 5' untranslated region and a 256-bp 3' untranslated region. The deduced amino acid sequences of MamMnSOD showed high sequence homology to mitochondrial MnSODs from crustaceans. Several motifs, including three mitochondrial MnSOD signatures, amino acid residues responsible for coordinating the manganese, and the putative active center, were almost completely conserved in the deduced amino acid sequences of MamMnSOD. The mRNA expression of MamMnSOD in the tissues of heart, liver, spleen, kidney, muscle, intestine, and gill was examined by quantitative real-time PCR; the highest expression was in the liver. Transcription of MamMnSOD was kinetically modulated in response to nitrite stress in liver and gill tissues. The purified recombinant MamMnSOD showed potent antioxidant activity. Polyclonal antibodies generated from the recombinant product of MamMnSOD were used to specifically identify the native protein in liver of M. amblycephala. Collectively, the findings of this study strongly suggested that MamMnSOD combats oxidative stress and cellular damage induced by nitrite, by detoxifying harmful reactive oxygen species in M. amblycephala.

Genomic structure, characterization and expression analysis of a manganese superoxide dismutase from pearl oyster Pinctada fucata

Manganese superoxide dismutase (MnSOD) is a major component of the cellular defense mechanisms against oxidative damage. We cloned and analyzed the expression pattern and genomic structure of the MnSOD gene of pearl oyster Pinctada fucata, hereafter designated as PoMnSOD. The full-length PoMnSOD cDNA was 1080 bp in length and consisted of a 5'-untranslated region (UTR) of 222 bp, a 3'-UTR of 318 bp with a polyadenylation signal (AATAAA) at 15 nucleotides upstream of the poly (A) tail, and an open reading frame (ORF) of 540 bp encoding a polypeptide of 180 amino acids with an estimated molecular mass of 20.4 kDa and a predicted pI of 6.72. Sequence analysis showed that PoMnSOD contained MnSOD family signatures F(44)NGGGHLNH(52), I(97)QGSGWGWLA(106) and D(138)VWEHAYY(145), four conserved residues for manganese metal binding (H(4), H(52), D(138) and H(142)), and two potential N-glycosylation sites (N(33) and N(51)). Homology analysis revealed that PoMnSOD shared 47.6-55.9% identity and 57.4-65.6% similarity to the other known PoMnSOD amino acid sequences. PoMnSOD genomic DNA was 5040 bp in length and contained three exons and two introns, which was a tripartite organization and coincided with the consensus GT-AG splicing rule. PoMnSOD promoter contained the various transcription factors associated with the immune modulation and stress responses. Quantitative RT-PCR analysis demonstrated that PoMnSOD was constitutively expressed in all detected tissues, and PoMnSOD mRNA expression was significantly up-regulated in intestine, mantle, gills, digestive gland and haemocytes after Vibrio alginolyticus injection. These results suggested that PoMoSOD was an acute-response protein involved in the innate immune responses of pearl oyster, and provided general information about the mechanisms of innate immune defense against bacterial infection in pearl oyster.

Molecular cloning and characterization of cat, gpx1 and Cu/Zn-sod genes in pengze crucian carp (Carassius auratus var. Pengze) and antioxidant enzyme modulation induced by hexavalent chromium in juveniles

Hexavalent chromium (Cr(6+)) is a common pollutant transient metal with high toxicity in the environment. The toxicological effects partly result from oxidative damage due to the production of excessive reactive oxygen species (ROS) in the reductive process of Cr(6+). To explore the influence of ROS induced directly by Cr(6+) on the oxidative stress generation and antioxidant system, the full length cDNAs of antioxidant-related genes cat, gpx1 and Cu/Zn-sod were successfully acquired from pengze crucian carp first and analyzed. Furthermore, the mRNA expression of the antioxidant genes encompassing catalase (cat), copper/zinc superoxide dismutase (Cu/Zn-sod) and glutathione peroxidase (gpx1), antioxidant enzyme activities of CAT, SOD, and GPx and total protein content were further studied in the gill, intestine and liver of pengze crucian carp (Carassius auratus var. Pengze) juveniles upon acute exposure to Cr(6+) at concentrations of 0.1, 1.0, 10 and 100 mg/L for 4 days. Differential significant changes of the antioxidant enzymes and gene expression were observed in different tissues. The findings contribute to better understanding the antioxidant mechanisms induced by Cr(6+) and selecting the organic-specific sensitive biomarkers to monitor the safety of the aquatic ecosystem.

A manganese superoxide dismutase with potent antioxidant activity identified from Oplegnathus fasciatus: genomic structure and transcriptional characterization

In this study, we describe the identification and characterization of manganese superoxide dismutase, an important antioxidant enzyme acting as the chief reactive oxygen species (ROS) scavenger, from rock bream Oplegnathus fasciatus (Of-mMnSOD) at genomic- and transcriptional-levels as well as the biological activity of recombinant protein. The Of-mMnSOD protein portrayed distinct MnSOD family features including signature motifs, metal association sites and the typical active site topology. It was also predicted to be localized in mitochondrial matrix. The Of-mMnSOD had a quinquepartite genome organization encompassing five exons interrupted by four introns. Comparison of its sequence and gene structure with that of other lineages emphasized its strong conservation among different vertebrates. The Of-mMnSOD was ubiquitously transcribed in different rock bream tissues with higher levels in blood cells and metabolically active tissues. Transcription of Of-mMnSOD was kinetically modulated in response to investigational challenges using mitogens (lipopolysaccharide and poly I:C) and live-pathogens (Edwardsiella tarda and rock bream irido virus) in blood cells and liver tissue. The purified recombinant Of-mMnSOD possessed potential antioxidant capacity and actively survived over a range of pH (7.5-11) and temperature (15-40 °C) conditions. Collectively, findings of this study suggest that Of-mMnSOD combats against oxidative stress and cellular damages induced by mitogen/pathogen-mediated inflammation, by detoxifying harmful ROS (O(2)(●-)) in rock bream.

Gamma irradiation-induced oxidative stress and developmental impairment in the hermaphroditic fish, Kryptolebias marmoratus embryo

This study investigated the effects of gamma radiation on the early developmental stages in hermaphroditic fish embryos of Kryptolebias marmoratus. The authors measured reactive oxygen species (ROS) level and antioxidant enzyme activities with the endpoint hatching rate after gamma irradiation of different embryonic stages. Then, the transcriptional changes of antioxidant enzyme-coding genes were evaluated by quantitative real-time reverse transcription polymerase chain reaction in response to gamma radiation on embryonic stages. Gamma radiation inhibited hatching rate and caused developmental impairment in a dose-dependent manner. Embryos showed tolerances in a developmental stage-dependent manner, indicating that early embryonic stages were more sensitive to the negative effects of gamma radiation than were later stages. After 5 Gy rate of radiation, the ROS level increased significantly at embryonic stages 2, 3, and 4 with a significant induction of all antioxidant enzyme activities. The expressions of glutathione S-transferase isoforms, catalase, superoxide dismutase (Mn-SOD, Cu/Zn-SOD), glutathione reductase, and glutathione peroxidase mRNA were upregulated in a dose-and-developmental stage-dependent manner. This finding indicates that gamma radiation can induce oxidative stress and subsequently modulates the expression of antioxidant enzyme-coding genes as one of the defense mechanisms. Interestingly, embryonic stage 1 exposed to gamma radiation showed a decreased expression in most antioxidant enzyme-coding genes, suggesting that this is also related to a lower hatching rate and developmental impairment. The results of this study provide a better understanding of the molecular mode of action of gamma radiation in aquatic organisms.

A manganese superoxide dismutase in blood clam Tegillarca granosa: molecular cloning, tissue distribution and expression analysis

Superoxide dismutase (SOD, EC 1.15.1.1) is one of the central enzymes involved in scavenging the high level of reactive oxygen species (ROS) by transforming O₂⁻ into hydrogen peroxide and oxygen. The full-length mitochondrial Mn-SOD cDNA of blood clam Tegillarca granosa (denoted as TgmMnSOD) was identified from haemocytes by homology cloning and rapid amplification of cDNA ends (RACE) approaches. The nucleotide sequence of TgmMnSOD consisted of 1106bp with a 5' UTR of 195bp, a 3' UTR of 227bp with a candidate polyadenylation signal sequence ATTAAA and a short polyA tail, and an open reading frame (ORF) of 648bp encoding a secreted polypeptide of 227 amino acids residues. The deduced amino acid sequence of TgmMnSOD shared significant homology to mMnSODs from other species, indicating that TgmMnSOD should be a novel member of the mMnSOD family. Several highly conserved motifs including three mMnSOD signatures, amino acid residues responsible for coordinating the manganese and the putative active center were almost completely conserved in the deduced amino acid of TgmMnSOD. The mRNA expression of TgmMnSOD in the tissues of mantle, foot, gill, haemocytes and hepatopancreas was examined by quantitative real-time PCR (qT-PCR) and mRNA transcripts of TgmMnSOD were mainly detected in hepatopancreas, haemocytes, and gill and weakly detected in the mantle and foot. The temporal expression of TgmMnSOD in haemocytes after heavy metal exposure revealed that TgmMnSOD could be induced by the three pollutants with different response profiles. The polyclonal antibodies generated from the recombinant product of TgmMnSOD could specifically identify not only the recombinant product, but also the native protein from haemocytes. The present results strongly suggested that TgmMnSOD was a cute response protein involved in marine heavy metal contaminants challenge in T. granosa.