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

Multi-omics analysis identifies sex-specific hepatic protein-metabolite networks in yellow catfish (Pelteobagrus fulvidraco) exposed to chronic hypoxia

Hypoxia disrupts the endocrine system of teleosts. The liver plays important roles in the endocrine system, energy storage, and metabolic processes. The aim of this study was to investigate the sex-specific hepatic response of yellow catfish under chronic hypoxia at the multi-omics level. Common hepatic responses in both sexes included the HIF-1 signaling pathway, glycolysis/gluconeogenesis, and steroid biosynthesis. Hypoxia dysregulated primary bile acid biosynthesis, lipid metabolism, and vitellogenin levels in female fish. Endoplasmic reticulum function in females also tended to be disrupted by hypoxia, as evidenced by significantly enriched pathways, including ribosome, protein processing in the endoplasmic reticulum, and RNA degradation. Other pathways, including the TCA cycle, oxidative phosphorylation, and Parkinson's and Huntington's disease, were highly enriched by hypoxia in male fish, suggesting that mitochondrial function was dysregulated. In both sexes of yellow catfish, the cell cycle was arrested and apoptosis was inhibited under chronic hypoxia. Multi-omics suggested that SLC2A5, CD209, LGMN, and NEDD8 served as sex-specific markers in these fish under chronic hypoxia. Our results provide insights into hepatic adaptation to chronic hypoxia and facilitate our understanding of sex-specific responses in fish.

Effects of acute hypoxia and reoxygenation on histological structure, antioxidant response, and apoptosis in razor clam Sinonovacula constricta

Hypoxia is one of the major environmental problems limiting the healthy development of intensive aquaculture. Marine benthic shellfish are encountering heightened problems related to hypoxic stress as a result of ongoing human activities and aquaculture operations. Razor clam Sinonovacula constricta, a commercially valuable shellfish, has not yet been reported in studies on physiological changes caused by hypoxia and reoxygenation. To understand the negative effects of hypoxia and reoxygenation on the clams, we set up two low-oxygen concentration groups (DO 2.0 mg/L and DO 0.5 mg/L) and assessed multiple aspects of oxidative damage to their hepatopancreas and gills. After the hypoxic stress, the two tissues of the razor clam suffered varying degrees of damage, including cell degeneration and disruption of mitochondrial cristae. After reoxygenation, the 2.0 mg/L group recovered substantially, but the clams in the 0.5 mg/L group still unrecovered. The activities of antioxidant enzymes (MDA, T-AOC, SOD, GPX, and CAT) in clams were considerably altered by acute hypoxia and reoxygenation. Briefly, there was a growing and then declining trend in MDA, T-AOC, and SOD activities in the hepatopancreas, whereas GPX and CAT activities showed the converse trend. In the hepatopancreas and gills, the level of anti-apoptotic gene Bcl-2 transcripts gradually decreased with the duration of hypoxia and increased following reoxygenation. However, changes in the transcript level of the pro-apoptotic gene Bax were in contrast to that of Bcl-2. The TUNEL assay revealed that hypoxia caused apoptosis. Furthermore, at DO 0.5 mg/L, the degree of apoptosis was more significant than at DO 2.0 mg/L, and hepatopancreatic apoptosis was more severe than gill apoptosis. Collectively, our findings imply that hypoxia induces oxidative stress, histological damage, and apoptosis in razor clams in a concentration-dependent and tissue-specific manner. These consequences serve as a reminder that prolonged recovery periods may be required for razor clams to fully recover from oxidative damage resulting from hypoxia-reoxygenation episodes.

Living in a hypoxic world: A review of the impacts of hypoxia on aquaculture

Hypoxia is a harmful result of anthropogenic climate change. With the expansion of global low-oxygen zones (LOZs), many organisms have faced unprecedented challenges affecting their survival and reproduction. Extensive research has indicated that oxygen limitation has drastic effects on aquatic animals, including on their development, morphology, behavior, reproduction, and physiological metabolism. In this review, the global distribution and formation of LOZs were analyzed, and the impacts of hypoxia on aquatic animals and the molecular responses of aquatic animals to hypoxia were then summarized. The commonalities and specificities of the response to hypoxia in aquatic animals in different LOZs were discussed lastly. In general, this review will deepen the knowledge of the impacts of hypoxia on aquaculture and provide more information and research directions for the development of fishery resource protection strategies.

Long-term hypoxia stress-induced oxidative stress, cell apoptosis, and immune response in the intestine of Pelteobagrus vachelli

Hypoxia is a common phenomenon in aquaculture. With the dissolved oxygen (DO) 3.75 ± 0.25 mg O2 /L for hypoxia group and 7.25 ± 0.25 mg O2 /L for control group for 30, 60, and 90 days, long-term hypoxia stress was used to investigate the oxidative stress, apoptosis, and immunity in the intestine of Pelteobagrus vachelli. According to the results of measurement of total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-PX), and catalase (CAT) activities and malondialdehyde (MDA) content, the oxidative stress ability of the intestine was activated at 30 days and impaired at 60 and 90 days. The upregulation of Bcl-2-associated x (Bax); downregulation of B cell lymphoma-2 (Bcl-2); increased activities of caspase-3, caspase-9, and Na+-K+-ATPase; decreased activities of succinate dehydrogenase (SDH); and the release of cytochrome c (Cyt-c) in mitochondria revealed that hypoxia induced the apoptosis. Moreover, heat shock protein 70 (HSP 70), heat shock protein 90 (HSP 90), immunoglobulin M (IgM), and C-lysozyme (C-LZM) were activated to inhibit apoptosis, but the immunoregulatory function might be damaged at 60 and 90 days. This study provides a theoretical foundation for understanding the mechanisms of hypoxia stress and aquaculture management of P. vachelli.

Resveratrol promotes mitochondrial energy metabolism in exercise-induced fatigued rats

BACKGROUND/OBJECTIVES

To investigate the effect and regulatory mechanism of resveratrol supplementation on the mitochondrial energy metabolism of rats with exercise-induced fatigue.

MATERIALS/METHODS

Forty-eight Sprague-Dawley male rats were divided randomly into a blank control group (C), resveratrol group (R), exercise group (E), and exercise and resveratrol group (ER), with 12 rats in each group. Group ER and group E performed 6-wk swimming training with 5% wt-bearing, 60 min each time, 6 days a wk. Group ER was given resveratrol 50 mg/kg by gavage one hour after exercise; group R was only given resveratrol 50 mg/kg by gavage; group C and group E were fed normally. The same volume of solvent was given by gavage every day.

RESULTS

Resveratrol supplementation could reduce the plasma blood urea nitrogen content, creatine kinase activity, and malondialdehyde content in the skeletal muscle, increase the total superoxide dismutase activity in the skeletal muscle, and improve the fatigue state. Resveratrol supplementation could improve the activities of Ca²⁺-Mg²⁺-ATPase, Na⁺-K⁺-ATPase, succinate dehydrogenase, and citrate synthase in the skeletal muscle. Furthermore, resveratrol supplementation could up-regulate the sirtuin 1 (SIRT1)-proliferator-activated receptor gamma coactivator-1α (PGC-1α)-nuclear respiratory factor 1 pathway.

CONCLUSIONS

Resveratrol supplementation could promote mitochondrial biosynthesis via the SIRT1/PGC-1α pathway, increase the activity of the mitochondrial energy metabolism-related enzymes, improve the antioxidant capacity of the body, and promote recovery from exercise-induced fatigue.

Effects of saline immersion on the physiological alterations of grass goldfish (Carassius auratus) during subsequent recovery in freshwater

The present work aims to evaluate the tolerance, osmoregulation, metabolism, and antioxidant ability of saline water immersed grass goldfish (Carassius auratus) during the recovery in freshwater. Grass goldfish (38.15 ± 5.48g) acclimated in freshwater were immersed by salinities (0‰, 20‰ and 30‰) for different time durations (10, 20, 30 and 60 min); and the physiological responses were measured during freshwater recovery. The blood osmolalities were not significantly different at any group fish, while whereas the decline of Na⁺ concentration and the ratio of Na⁺/Cl^- as well as the rise of Cl^- concentration was observed in saline treated fish. Soon after freshwater recovery, the transcription of NKA-α and NKA-β mRNA in gills of salinity 20 immersed fish elevated significantly and then decreased, whereas no obvious changes were detected in salinity 30 treated fish. Till 24h post freshwater recovery, gill Na+/K+-ATPase activities in saline treated fish were lower than control group except for the fish immersed by salinity 20 for 10-30 min. At 24h of recovery, cortisol levels in salinity 20 immersed fish were lower than salinity 30 treated fish, but remained higher than control. As for serum lactic acid, fish treated by salinity 20 for 10 or 20 min did not show any fluctuation. However, higher lactic acid contents were detected in all other five salinity treated groups during recovery. Generally, at 24 h of recovery, salinity 20 treated fish exhibited higher SOD and CAT activities than fish immersed by salinity 30. In summary, grass goldfish could survive by immersion in salinity 20 less than 60 min or salinity 30 less than 30min, even though immersion by salinity 20 could minimize the negative effects.

Alteration of antioxidant status, glucose metabolism, and hypoxia signal pathway in Eirocheir sinensis after acute hypoxic stress and reoxygenation

Dissolved oxygen (DO) is crucial for the survival of Chinese mitten crab (Eirocheir sinensis); low DO levels adversely affect the health of these crabs. In this study, we evaluated the underlying response mechanism of E. sinensis to acute hypoxic stress by analyzing antioxidant parameters, glycolytic indicators, and hypoxia signaling factors. The crabs were exposed to hypoxia for 0, 3, 6, 12, and 24 h and reoxygenated for 1, 3, 6, 12, and 24 h. The hepatopancreas, muscle, gill, and hemolymph were sampled at different exposure times to detect the biochemical parameters and gene expression. The results showed that the activity of catalase, antioxidants, and malondialdehyde in tissues significantly increased under acute hypoxia and gradually decreased during the reoxygenation phase. Under acute hypoxic stress, glycolysis indices, including hexokinase (HK), phosphofructokinase, pyruvate kinase (PK), pyruvic acid (PA), lactate dehydrogenase (LDH), lactic acid (LA), succinate dehydrogenase (SDH), glucose, and glycogen in the hepatopancreas, hemolymph, and gills increased to varying degrees but recovered to the control levels after reoxygenation. Gene expression data showed that hypoxia signaling pathway-related genes, including hypoxia-inducible factor-1α/β (HIF1α/β), prolyl hydroxylase (PHD), factor inhibiting hypoxia-inducible factor (FIH), and glycolysis-related factors (HK and PK) were upregulated, showing that the HIF signaling pathway was activated under hypoxic conditions. In conclusion, acute hypoxic exposure activated the antioxidant defense system, glycolysis, and HIF pathway to respond to adverse conditions. These data contribute to elucidating the defense and adaptive mechanisms of crustaceans to acute hypoxic stress and reoxygenation.

Blood redistribution preferentially protects vital organs under hypoxic stress in Pelteobagrus vachelli

Blood redistribution occurs in mammals under hypoxia but has not been reported in fish. This study investigated the tissue damage, hypoxia-inducible factor (HIF) activation level, and blood flow changes in the brain, liver, and muscle of Pelteobagrus vachelli during the hypoxia process for normoxia-hypoxia-asphyxia. The results showed that P. vachelli has tissue specificity in response to hypoxic stress. Cerebral blood flow increased with less damage than in the liver and muscle, suggesting that P. vachelli may also have a blood redistribution mechanism in response to hypoxia. It is worth noting that severe hypoxia can lead to a sudden increase in the degree of brain tissue damage. In addition, higher dissolved oxygen levels activate HIF and may have contributed to the reduced damage observed in the brain. This study provides basic data for investigating hypoxic stress in fish.

Multi-omics analysis revealed the brain dysfunction induced by energy metabolism in Pelteobagrus vachelli under hypoxia stress

Hypoxia in water environment has become increasingly frequent and serious due to global warming and environmental pollution. Revealing the molecular mechanism of fish hypoxia adaptation will help to develop markers of environmental pollution caused by hypoxia. Here, we used a multi-omics method to identify the hypoxia-associated mRNA, miRNA, protein, and metabolite involved in various biological processes in Pelteobagrus vachelli brain. The results showed that hypoxia stress caused brain dysfunction by inhibiting energy metabolism. Specifically, the biological processes involved in energy synthesis and energy consumption are inhibited in P. vachelli brain under hypoxia, such as oxidative phosphorylation, carbohydrate metabolism and protein metabolism. Brain dysfunction is mainly manifested as blood-brain barrier injury accompanied by neurodegenerative diseases and autoimmune diseases. In addition, compared with previous studies, we found that P. vachelli has tissue specificity in response to hypoxia stress and the muscle suffers more damage than the brain. This is the first report to the integrated analysis of the transcriptome, miRNAome, proteome, and metabolome in fish brain. Our findings could provide insights into the molecular mechanisms of hypoxia, and the approach could also be applied to other fish species. DATA AVAILABILITY: The raw data of transcriptome has been uploaded to NCBI database (ID: SUB7714154 and SUB7765255). The raw data of proteome has been uploaded to ProteomeXchange database (PXD020425). The raw data of metabolome has been uploaded to Metabolight (ID: MTBLS1888).

Protective effect and mechanism of Polygonatum kingianum against hypoxia-induced injury

Background

Hypoxia is an essential cause of fatigue and aging, and is associated with the occurrence and development of many diseases. Polygonatum kingianum (PK) is a deficiency-nourishing Chinese herbal medicine utilized as both medicine and food, and it has long been used to ameliorate human conditions associated with fatigue and aging over 2000 years in China. PK is an important genuine-medicinal-materials cultivated in Yunnan, China, and is used by the Bai, Wa, and Zhuang nationalities as a traditional medicine for enhancing immunity, anti-fatigue, and anti-aging, while the preventive effect of PK on hypoxia-induced injury and the underlying mechanism are indefinite.

Aim of the study

The present study aimed to evaluate the anti-hypoxia efficacy and understand the corresponding mechanism of PK water extract.

Materials and methods

The main active ingredients and targets of PK were predicted using network pharmacology, and the anti-hypoxia activities of Gracillin and Liquiritigenin were verified by in vitro experiments. The pharmacodynamic experiments were conducted to evaluate the major signal pathways of PK for detecting anti-hypoxia activity.

Results

Fifty active ingredients and 371 potential targets were screened by network pharmacology, then, we confirmed that Gracillin and Liquiritigenin were the main active components of PK to exert anti-hypoxia effect in vitro. The pharmacodynamic experiments revealed that PK enhanced the extension rate of the survival time (ERST) and regulated the targets-related biochemical parameters of rats under hypoxia, showing significant anti-hypoxia effects on rats.

Conclusion

The network pharmacology results suggested that PK exerts its anti-hypoxia effect through a multi-component and multi-target manner. Simultaneously, we also observed that Gracillin (saponins) and Liquiritigenin (flavonoids) are the main active components of PK to play a role in anti-hypoxia. The anti-hypoxia effect of PK could be associated with scavenging excess free radicals, maintaining the activities of antioxidant enzymes, and inhibiting oxidative stress due to lipid peroxidation. These findings provide insight into the Polygonatum kingianum as promising medicines or healthcare products for preventing and treating hypoxia.

A high-quality chromosome-level genome assembly of Pelteobagrus vachelli provides insights into its environmental adaptation and population history

Pelteobagrus vachelli is a freshwater fish with high economic value, but the lack of genome resources has severely restricted its industrial development and population conservation. Here, we constructed the first chromosome-level genome assembly of P. vachelli with a total length of approximately 662.13 Mb and a contig N50 was 14.02 Mb, and scaffolds covering 99.79% of the assembly were anchored to 26 chromosomes. Combining the comparative genome results and transcriptome data under environmental stress (high temperature, hypoxia and Edwardsiella. ictaluri infection), the MAPK signaling pathway, PI3K-Akt signaling pathway and apelin signaling pathway play an important role in environmental adaptation of P. vachelli, and these pathways were interconnected by the ErbB family and involved in cell proliferation, differentiation and apoptosis. Population evolution analysis showed that artificial interventions have affected wild populations of P. vachelli. This study provides a useful genomic information for the genetic breeding of P. vachelli, as well as references for further studies on fish biology and evolution.

An accidental discovery of mannan-oligosaccharide's protection effect against air exposure and its potential mechanism in hybrid grouper (Epinephelus lanceolatus ♂ × Epinephelus fuscoguttatus ♀)

The original objective was to explore the potential benefiting effects of three prebiotics in hybrid grouper (Epinephelus lanceolatus♂ × Epinephelus fuscoguttatus♀). Therefore, three experimental diets (basal diet + 1% fructooligosaccharide, Diet F; basal diet + 1% inulin, Diet I; basal diet + 0.3% mannan-oligosaccharide, Diet M) and one basal diet (Diet C) were prepared and a feeding trial was conducted. However, at the end of the fourth week into the feeding experiment, a water-leaking accident occurred and fishes of all groups went through an unexpected air exposure event. Surprisingly, different prebiotic-supplemented groups showed significantly different air exposure tolerance: the mortality of M group was significantly lower (P ≤ 0.05) than all the other groups. Examination of antioxidant, non-specific immunity, and stress parameters revealed that comparing to control group, M group showed significantly increased catalase (CAT), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities, decreased superoxide dismutase (SOD) activity, and similar cortisol level (P ≤ 0.05). Real-time PCR experiment revealed that M group significantly increased the expression of CAT, glutathione peroxidase (GPx), and manganese superoxide dismutase (MnSOD) genes in head kidney (P ≤ 0.05). Overall, M exhibited the best anti-air exposure/antioxidative stress effects among the three prebiotics and could be considered a promising feed additive to relieve air exposure/oxidative stress in hybrid grouper culture.

Hypoxia-induced oxidative stress and apoptosis in gills of scaleless carp (Gymnocypris przewalskii)

Scaleless carp (Gymnocypris przewalskii) are well adapted to low oxygen environment, but their specific adaptation mechanism to hypoxic condition remains unclear. The gill is an important respiratory organ that plays a crucial role in regulating hypoxic stress. Here, we established fish hypoxic stress model, as well as investigated oxidative stress, apoptotic responses, and relative enzyme activities in the gills of scaleless carp after exposure to various levels of hypoxic stress. The results demonstrated that gill lamellar height and basal length increased significantly under severe hypoxic stress, and interval lengths between lamellae increased significantly under hypoxic stress. Furthermore, lamellar epithelial cells underwent apoptosis, cytoplasmic contraction, and mitochondrial expansion, and the number of apoptotic cells increased significantly after exposure to severe hypoxic stress for 24 h. Subsequently, Bcl-2 and Caspase 3 mRNA levels, as well as Bcl-2/Bax expression ratio were significantly increased after exposure to severe hypoxic stress for 24 h, indicating upregulation of anti-apoptotic processes. Moreover, malondialdehyde and hydrogen peroxide levels were significantly increased after exposure to hypoxic stress for 24 h. Superoxide dismutase activity increased significantly after exposure to severe hypoxia for 8 h and then decreased, while glutathione peroxidase activity and total antioxidant capacity increased significantly under hypoxic stress. Taken together, the results indicated that scaleless carp gills respond to acute hypoxic conditions by undergoing lamellar morphology remodeling, enhanced apoptosis, and increased antioxidant enzymatic activity. The study findings provided new insight into the adaptation mechanisms of scaleless carp in response to hypoxic challenge.

Tandem Mass Tagging-Based Quantitative Proteomics Analysis Reveals Damage to the Liver and Brain of Hypophthalmichthys molitrix Exposed to Acute Hypoxia and Reoxygenation

Aquaculture environments frequently experience hypoxia and subsequent reoxygenation conditions, which have significant effects on hypoxia-sensitive fish populations. In this study, hepatic biochemical activity indices in serum and the content of major neurotransmitters in the brain were altered markedly after acute hypoxia and reoxygenation exposure in silver carp (Hypophthalmichthys molitrix). Proteomics analysis of the liver showed that a number of immune-related and cytoskeletal organization-related proteins were downregulated, the ferroptosis pathway was activated, and several antioxidant molecules and detoxifying enzymes were upregulated. Proteomics analysis of the brain showed that somatostatin-1A (SST1A) was upregulated, dopamine-degrading enzyme catechol O methyltransferase (COMT) and ferritin, heavy subunit (FerH) were downregulated, and the levels of proteins involved in the nervous system were changed in different ways. In conclusion, these findings highlight that hypoxia–reoxygenation has potential adverse effects on growth, locomotion, immunity, and reproduction of silver carp, and represents a serious threat to liver and brain function, possibly via ferroptosis, oxidative stress, and cytoskeleton destruction in the liver, and abnormal expression of susceptibility genes for neurodegenerative disorders in the brain. Our present findings provide clues to the mechanisms of hypoxia and reoxygenation damage in the brain and liver of hypoxia-sensitive fish. They could also be used to develop methods to reduce hypoxia or reoxygenation injury to fish.

Effect of Dietary Plant Feedstuffs and Protein/Carbohydrate Ratio on Gilthead Seabream (Sparus aurata) Gut Health and Functionality

This study investigated, for the first time, the integrated effects of dietary protein source and protein/carbohydrate (P/CH) ratio on gilthead seabream gut histomorphology, microbiota composition, digestive enzymes activity, and immunological and oxidative stress-related gene expressions. Four isolipidic diets: two fishmeal-based (FM) and two plant feedstuff (PF)-based diets, with P/CH ratios of 50/10 or 40/20 each (FM-P50/CH10; FM-P40/CH20; PF-P50/CH10; PF-P40/CH20), were tested. PF-based diets lead to more histomorphological alterations than FM-based diets. P/CH ratio had no relevant effect on gut histomorphology. Gut mucosa of fish fed PF-based diets presented a higher number of operational taxonomic units, and richness and diversity indices, while the P/CH ratio did not affect those parameters. The α-amylase activity was lower in fish fed with PF-based diets and in fish fed the P40/CH20 diets. Regarding the immune-related genes, only cyclooxygenase-2 was affected, being higher in fish fed the P50/CH10 diets than the P40/CH20 diets. Fish fed the FM-based diets presented higher expression of glutathione reductase and glutathione peroxidase, while fish fed the P50/CH10 diet had higher expression of superoxide dismutase. In conclusion, PF-based diets can compromise gut absorptive and digestive metabolism, but decreasing the dietary P/CH ratio had little effect on the parameters measured.

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.

Molecular Characterization and Response of Prolyl Hydroxylase Domain (PHD) Genes to Hypoxia Stress in Hypophthalmichthys molitrix

Simple Summary

Hypoxia is a common challenge for aquatic organisms, and prolyl hydroxylase domain (PHD) proteins play important roles in hypoxic adaptation by regulating the stability of the hypoxia-inducible factor 1 alpha subunit (HIF-1α). In this study, the full-length cDNAs of three PHD genes were obtained from Hypophthalmichthys molitrix, which is an important freshwater fish and sensitive to low oxygen tension. The amino acid sequence analysis and phylogenetic analysis of PHDs were performed among various species. Furthermore, the expression patterns and the transcriptional responses of H. molitrix PHD genes to acute hypoxia, continued hypoxia, and reoxygenation were explored in different tissues. Our study preliminarily explored the physiological regulation functions of PHD genes at the transcriptional level when addressing the hypoxic challenge and provided a foundation for future systematic explorations of the molecular mechanisms underlying hypoxia adaptation in silver carp.

Abstract

As an economically and ecologically important freshwater fish, silver carp (Hypophthalmichthys molitrix) is sensitive to low oxygen tension. Prolyl hydroxylase domain (PHD) proteins are critical regulators of adaptive responses to hypoxia for their function of regulating the hypoxia inducible factor-1 alpha subunit (HIF-1α) stability via hydroxylation reaction. In the present study, three PHD genes were cloned from H. molitrix by rapid amplification of cDNA ends (RACE). The total length of HmPHD1, HmPHD2, and HmPHD3 were 2981, 1954, and 1847 base pair (bp), and contained 1449, 1080, and 738 bp open reading frames (ORFs) that encoded 482, 359, and 245 amino acids (aa), respectively. Amino acid sequence analysis showed that HmPHD1, HmPHD2, and HmPHD3 had the conserved prolyl 4-hydroxylase alpha subunit homolog domains at their C-termini. Meanwhile, the evaluation of phylogeny revealed PHD2 and PHD3 of H. molitrix were more closely related as they belonged to sister clades, whereas the clade of PHD1 was relatively distant from these two. The transcripts of PHD genes are ubiquitously distributed in H. molitrix tissues, with the highest expressional level of HmPHD1 and HmPHD3 in liver, and HmPHD2 in muscle. After acute hypoxic treatment for 0.5 h, PHD genes of H. molitrix were induced mainly in liver and brain, and different from HmPHD1 and HmPHD2, the expression of HmPHD3 showed no overt tissue specificity. Furthermore, under continued hypoxic condition, PHD genes exhibited an obviously rapid but gradually attenuated response from 3 h to 24 h, and upon reoxygenation, the transcriptional expression of PHD genes showed a decreasing trend in most of the tissues. These results indicate that the PHD genes of H. molitrix are involved in the early response to hypoxic stress, and they show tissue-specific transcript expression when performing physiological regulation functions. This study is of great relevance for advancing our understanding of how PHD genes are regulated when addressing the hypoxic challenge and provides a reference for the subsequent research of the molecular mechanisms underlying hypoxia adaptation in silver carp.

Effects of acute hypoxia and reoxygenation on oxygen sensors, respiratory metabolism, oxidative stress, and apoptosis in hybrid yellow catfish "Huangyou-1"

The regulation mechanism of the hybrid yellow catfish "Huangyou-1" was assessed under conditions of hypoxia and reoxygenation by examination of oxygen sensors and by monitoring respiratory metabolism, oxidative stress, and apoptosis. The expressions of genes related to oxygen sensors (HIF-1α, HIF-2α, VHL, HIF-1β, PHD2, and FIH-1) were upregulated in the brain and liver during hypoxia, and recovered compared with control upon reoxygenation. The expressions of genes related to glycolysis (HK1, PGK1, PGAM2, PFK, and LDH) were increased during hypoxia and then recovered compared with control upon reoxygenation. The mRNA levels of CS did not change during hypoxia in the brain and liver, but increased during reoxygenation. The mRNA levels of SDH decreased significantly only in the liver during hypoxia, but later increased compared with control upon reoxygenation in both tissues. Under hypoxic conditions, the expressions of genes related to oxidative stress (SOD1, SOD2, GSH-Px, and CAT) and the activity of antioxidant enzymes (SOD, CAT, and GSH-Px) and MDA were upregulated compared with control. The expressions of genes related to apoptosis (Apaf-1, Bax, Caspase 3, Caspase 9, and p53) were higher than those in control during hypoxic exposure, while the expressions of Bcl-2 and Cyt C were decreased. The findings of the transcriptional analyses will provide insights into the molecular mechanisms of hybrid yellow catfish "Huangyou-1" under conditions of hypoxia and reoxygenation. Overall, these findings showed that oxygen sensors of "Huangyou-1" are potentially useful biomarkers of environmental hypoxic exposure. Together with genes related to respiratory metabolism, oxidative stress and apoptosis occupy a quite high position in enhancing hypoxia tolerance. Our findings provided new insights into the molecular regulatory mechanism of hypoxia in "Huangyou-1."

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.

A high-density SNP-based genetic map and several economic traits-related loci in Pelteobagrus vachelli

BACKGROUND

A high-density genetic linkage map is essential for QTL fine mapping, comparative genome analysis, identification of candidate genes and marker-assisted selection in aquaculture species. Pelteobagrus vachelli is a very popular commercial species in Asia. However, some specific characters hindered achievement of the traditional selective breeding based on phenotypes, such as lack of large-scale genomic resource and short of markers tightly associated with growth, sex determination and hypoxia tolerance related traits.

RESULTS

By making use of 5059 ddRAD markers in P. vachelli, a high-resolution genetic linkage map was successfully constructed. The map' length was 4047.01 cM by using an interval of 0.11 cm, which is an average marker standard. Comparative genome mapping revealed that a high proportion (83.2%) of markers with a one-to-one correspondence were observed between P. vachelli and P. fulvidraco. Based on the genetic map, 8 significant genome-wide QTLs for 4 weight, 1 body proportion, 2 sex determination, and 1 hypoxia tolerance related traits were detected on 4 LGs. Some SNPs from these significant genome-wide QTLs were observably associated with these phenotypic traits in other individuals by Kompetitive Allele Specific PCR. In addition, two candidate genes for weight, Sipa1 and HSD11B2, were differentially expressed between fast-, medium- and slow-growing P. vachelli. Sema7a, associated with hypoxia tolerance, was induced after hypoxia exposure and reoxygenation.

CONCLUSIONS

We mapped a set of suggestive and significant QTLs as well as candidate genes for 12 growth, 1 sex determination and 1 hypoxia tolerance related traits based on a high-density genetic linkage map by making use of SNP markers for P. fulvidraco. Our results have offered a valuable method about the much more efficient production of all-male, fast growth and hypoxia tolerance P. vachelli for the aquaculture industry.

Identification of Hypoxia-Specific Biomarkers in Salmonids Using RNA-Sequencing and Validation Using High-Throughput qPCR

Identifying early gene expression responses to hypoxia (i.e., low dissolved oxygen) as a tool to assess the degree of exposure to this stressor is crucial for salmonids, because they are increasingly exposed to hypoxic stress due to anthropogenic habitat change, e.g., global warming, excessive nutrient loading, and persistent algal blooms. Our goal was to discover and validate gill gene expression biomarkers specific to the hypoxia response in salmonids across multi-stressor conditions. Gill tissue was collected from 24 freshwater juvenile Chinook salmon (Oncorhynchus tshawytscha), held in normoxia [dissolved oxygen (DO) > 8 mg L^-1] and hypoxia (DO = 4‒5 mg L^-1) in 10 and 18° temperatures for up to six days. RNA-sequencing (RNA-seq) was then used to discover 240 differentially expressed genes between hypoxic and normoxic conditions, but not affected by temperature. The most significantly differentially expressed genes had functional roles in the cell cycle and suppression of cell proliferation associated with hypoxic conditions. The most significant genes (n = 30) were selected for real-time qPCR assay development. These assays demonstrated a strong correlation (r = 0.88; P < 0.001) between the expression values from RNA-seq and the fold changes from qPCR. Further, qPCR of the 30 candidate hypoxia biomarkers was applied to an additional 322 Chinook salmon exposed to hypoxic and normoxic conditions to reveal the top biomarkers to define hypoxic stress. Multivariate analyses revealed that smolt stage, water salinity, and morbidity status were relevant factors to consider with the expression of these genes in relation to hypoxic stress. These hypoxia candidate genes will be put into application screening Chinook salmon to determine the identity of stressors impacting the fish.

Comparative Transcriptome Analysis of Gill Tissue in Response to Hypoxia in Silver Sillago (Sillago sihama)

Silver sillago (Sillago sihama) is a commercially important marine fish species in East Asia. In this study, we compared the transcriptome response to hypoxia stress in the gill tissue of S. sihama. The fish were divided into four groups, such as 1 h of hypoxia (hypoxia1h, DO = 1.5 ± 0.1 mg/L), 4 h of hypoxia (hypoxia4h, DO = 1.5 ± 0.1 mg/L), 4 h of reoxygen (reoxygen4h, DO = 8.0 ± 0.2 mg/L) after 4 h of hypoxia (DO = 1.5 mg/L), and normoxia or control (DO = 8.0 ± 0.2 mg/L) groups. Compared to the normoxia group, a total of 3550 genes were identified as differentially expressed genes (DEGs) (log₂foldchange > 1 and padj < 0.05), including 1103, 1451 and 996 genes in hypoxia1h, hypoxia4h and reoxygen4h groups, respectively. Only 247 DEGs were differentially co-expressed in all treatment groups. According to Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, DEGs were significantly enriched in steroid biosynthesis, biosynthesis of amino acids, glutathione metabolism and metabolism of xenobiotics by cytochrome P450, ferroptosis and drug metabolism-cytochrome P450 pathways. Of these, the cytochrome P450 (CYP) and glutathione S-transferase (GST) gene families were widely expressed. Our study represents the insights into the underlying molecular mechanisms of hypoxia stress.

Protection of teprenone against hypoxia and reoxygenation stress in stomach and intestine of Lateolabrax maculatus

Teprenone (geranylgeranylacetone) is one kind of safe and effective agent in gastrointestinal mucosa, which have been widely used in human and veterinary, but rarely used in aquaculture animals. In this study, Lateolabrax maculatus, an important economic fish species in southern China, was taken as the object of study to investigate the protective effect of teprenone on intestinal stress. The present study was designed to investigate the potential mechanism underlying the protection offered by teprenone to protect the gastrointestinal tract against hypoxia and reoxygenation injury of L. maculatus. (a) For oxidative stress parameters, SOD, CAT, and T-AOC in control group were higher than those in teprenone group. MDA content was significantly higher than that in teprenone group at N and 12h time points in intestine (P < 0.05), and at 12, 24, and 48 h time points in stomach. (b) For immune-associated proteins, LZM activity in the control group was lower than that in the teprenone group, and the difference between the two groups in stomach and intestine was significant at 12.48 h and 6.48 h time points, respectively (P < 0.05). Compared with time point N, the content of HSP70 in the control group increased at 0 h in intestine. At 0-48 h, intestine HSP70 content in the control group showed a gradually decreasing trend, which was higher than that in the teprenone group. (c) For apoptosis-related factors, the activity of Cyt-C, caspase9, and caspase3 increased first and then decreased in both groups. The content of Cyt-C in the control group was significantly higher than that in the teprenone group at N-3.6 h, and 3.48 h time points in stomach and intestine, respectively (P<0.05). The activity of caspase9 and caspase3 was higher than that in the teprenone group at N-48 h. Results indicated that acute hypoxia and reoxygenation cause the expression levels of oxidative stress and apoptosis-related factors in the stomach and intestine increased first and then decreased within 0-48 h. Acute hypoxia and reoxygenation also that causes the level of nonspecific immunity decreased first and then increased. A total of 400-mg/kg treatment of teprenone can protect stomach and intestinal tissues to a certain extent. It can effectively protect oxidative stress and apoptosis within 0-48 h after acute hypoxia and reoxygenation and enhance non-specific immunity.

Pre-hypoxia exposure inhibited copper toxicity by improving energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea

This study investigated the effects of moderate hypoxia pre-exposure on energy metabolism, antioxidant defence and mitophagy in the liver of the large yellow croaker Larimichthys crocea exposed to Cu. Fish were pre-exposed to either normoxia or hypoxia (~3.0 mg L^-1, 42% O₂ saturation) for 48 h, and subsequently were subjected to either control (without Cu addition) or Cu (168 μg L^-1) under normoxic conditions for another 48 h. Copper exposure under normoxia induced Cu toxicity that increased mortality, the production of reactive oxygen species (ROS) and malondialdehyde, and aberrant hepatic mitochondrial ultrastructure. Interestingly, hypoxia pre-exposure improved energy metabolism, antioxidant ability and mitophagy response, and reduced the Cu content to inhibit Cu toxicity, reflecting the enhanced survival rate and reduced oxidative damage. In these processes, hypoxia-inducible factor-1α (HIF-1α), transcription factors NFE2-related nuclear factor 2 (Nrf2), and forkhead box O-3 (FoxO3) mRNA levels were correlated with expression of genes related to energy metabolism, antioxidant defence and mitophagy, respectively, indicating HIF-1α, Nrf2, and FoxO3 are required for the induction of their respective target genes. Overall, moderate hypoxia pre-exposure was able to generate adaptive responses to mitigate Cu-induced toxicological effects, underlining a central role of hormesis.

Interactive effect of thermal and hypoxia on largemouth bass (Micropterus salmoides) gill and liver: Aggravation of oxidative stress, inhibition of immunity and promotion of cell apoptosis

High temperatures and low oxygen in aquatic environments, such as intensive aquaculture or in natural watersheds, inevitably cause stress in fish. Fish are exposed to high temperatures during the summer, which exacerbates hypoxia. Hypoxia (1.2 ± 0.2 mg/L) under 20 °C (20 HG) and 26 °C (26 HG) was simulated to induce stress in largemouth bass (Micropterus salmoides). Related enzymes and genes involved in antioxidant, immune, and apoptotic responses were selected to explore the interactive effects of temperature and hypoxia on largemouth bass. The results showed that malondialdehyde (MDA) levels in plasma, gill, and liver increased in the 26 HG (p < 0.05). Liver superoxide dismutase (SOD) activity increased in the 26 HG. Peak SOD (SOD1, SOD2, SOD3a, and SOD3b), CAT, and GSH-Px mRNA levels in the gill and liver were observed at 12-24 h of stress. The levels of gill and liver total antioxidant capacity, catalase (CAT), glutathione peroxidase (GSH-Px) activities and other enzyme activities and genes in the 26 HG were higher than those in the 20 HG (p < 0.05). The gill and liver acid phosphatase and alkaline phosphatase activities increased with time in the 26 HG (p < 0.05), while gill and liver lysozyme activities in the 26 HG were lower than those in the 20 HG (p < 0.05). Tumor necrosis factor-α mRNA level was upregulated in the gill and downregulated in the liver at 24 h in the 26 HG. Interleukin (IL)-1β and IL-8 mRNA levels were upregulated in the gill and liver in the 26 HG at 24 h, whereas IL-15 mRNA level was downregulated in the 26 HG at 12 h. Transforming growth factor-β1 mRNA level was upregulated in the gill in the 20 HG at 24 h, but downregulated in gill and liver in the 26 HG at 24 h. Similarly, IL-10, Hepcidin-1, and Hepcidin-2 showed lower expression levels in the 26 HG. Gill and liver caspase-3 activities were higher in the 26 HG (p < 0.05), and gill caspase-3 activity was higher than that in the liver. The mRNA levels of proapoptotic genes (caspase-3, caspase-8, and caspase-9) were higher in the 26 HG. The present study demonstrates the interactive effects of temperature and hypoxia on stress in largemouth bass gill and liver. These results will be helpful to understand the mechanisms of stress induced by temperature and hypoxia in fish and provide a theoretical basis for aquaculture management.

Transcriptome and physiology analysis identify key metabolic changes in the liver of the large yellow croaker (Larimichthys crocea) in response to acute hypoxia

The large yellow croaker (Larimichthys crocea) is one of the most important marine economic fish in the southeast coast of China. However, hypoxia stress become a major obstacle to the benign development of L. crocea industry. To understand the energy metabolism mechanism adapted to hypoxia, we analyzed the transcriptome and physiology of L. crocea liver in response to hypoxia stress for different durations. We obtained 243,756,080 clean reads, of which 83.38% were successfully mapped to the reference genome of L. crocea. The heat map analysis showed that genes encoding enzymes involved in glycolysis/gluconeogenesis were significantly upregulated at various time points. Moreover, genes encoding enzymes related to the citrate cycle, oxidative phosphorylation, and amino acid metabolism were significantly downregulated at 6 and 24 h, but upregulated at 48 and 96 h. The change of liver in physiology processes, including respiratory metabolism, and activities of the carbohydrate metabolism enzymes showed a similar trend. The results revealed that the respiratory metabolism of L. crocea was mainly anaerobic within 24 h of hypoxia stress, and aerobic metabolism was dominant after 24 h. Carbohydrate metabolism plays a crucial role in energy supply and amino acid metabolism is an important supporting character to cope with acute hypoxia stress. There was no significant change in lipid utilization under short-term acute stress. This study increases our understanding of the energy metabolism mechanism of the hypoxia response in fish and provides a useful resource for L. crocea genetics and breeding.

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.

iTRAQ analysis of liver immune-related proteins from darkbarbel catfish (Pelteobagrus vachelli) infected with Edwardsiella ictaluri

Edwardsiella ictaluri causes enteric septicemia of catfish (ESC), a major disease occurring in these siluriform fish. As the liver is an important organ for defending against bacterial pathogens in fish, this study aimed to determine the liver immune response at the protein level. The differential proteomes of the darkbarbel catfish liver in response to E. ictaluri infection were identified with isobaric tags for relative and absolute quantitation (iTRAQ) labeling followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Using a 1.2-fold change in expression as a physiologically significant benchmark, a total of 819 differentially expressed proteins were reliably quantified using iTRAQ analysis, including 6 up-regulated proteins and 813 down-regulated proteins. GO enrichment analysis indicated that the "complement activation, alternative pathway" and "complement activation, classical pathway" were significantly enriched. KEGG enrichment analysis indicated the "antigen processing and presentation" and "bacterial secretion system" were significantly enriched. We selected the 6 up-regulated proteins and 10 immune-related down-regulated proteins for validation using real-time PCR. The 10 immune-related proteins included complement component C1r, C3, C5, C7, and C9 and plasma protease C1 inhibitor (C1-INH), signal recognition particle 54 kDa protein (SRP54), SRP receptor, proteasome activator complex subunit 1 (PSME1) and major histocompatibility complex class I (MHC class I) were selected from the GO clusters and KEGG pathways. The variations in mRNA expression for these genes were similar to the results of iTRAQ. This is the first report detailing the proteome response in the darkbarbel catfish liver during E. ictaluri infection and markedly contributes to our understanding of the defense mechanisms in the livers of darkbarbel catfish.

The improved energy metabolism and blood oxygen-carrying capacity for pufferfish, Takifugu fasciatus, against acute hypoxia under the regulation of oxygen sensors

Hypoxia frequently occurs in aquatic ecosystem, which is influenced by salinity, water temperature, weather, and surface water runoff. In order to shed further light on the evolutionary and adaptive mechanisms in fish under hypoxic condition, the impact of acute hypoxia (1.63 ± 0.2 mg/L) and reoxygenation (7.0 ± 0.3 mg/L) on oxygen sensors, energy metabolism, and hematological indices was evaluated in Takifugu fasciatus. Data from transcriptional level analysis show that the expressions of genes related to oxygen sensors (HIF-1α, PHD2, and VHL) were upregulated in the brain and liver under hypoxia and recovered under reoxygenation. The upregulation of GLUT2, VEGF-A, and EPO in conjugation with VEGF-A protein and hematological indices conferred the rapid adjustments of cellular glucose uptake and blood oxygen-carrying capacities in pufferfish. Higher levels of glycolysis-related mRNAs (HK, PGK1, and PGAM2), HK activity, and proteins (PGK1 and PGAM2) were detected in the brain and liver under hypoxic condition compared with control. Interestingly, the expression of MDH1 at the mRNA, enzyme activity, and protein levels was significantly increased in the brain at 0 or 2 h and in the liver at 8 h under hypoxic condition. In addition, although the enzyme activity and mRNA expression of LDH in the brain were not significantly changed, a persistent upregulation was observed in the liver during hypoxia exposure. This study demonstrated that pufferfish could counterpoise the energetic demands and hematological functional properties evoked by oxygen sensors after hypoxia. Our findings provided new insights into the molecular regulatory mechanism of hypoxia in pufferfish.

Molecular Cloning and Expression of MnGST-1 and MnGST-2 from Oriental River Prawn, Macrobrachium nipponense, in Response to Hypoxia and Reoxygenation

The glutathione-S-transferase (GST) superfamily includes seven classes, and different classes have different functions. GST superfamily members function in various processes including detoxification of xenobiotics, protection against oxidative damage, and intracellular transport of hormones, endogenous metabolites, and exogenous chemicals. Herein, to elucidate the tissue-specific expression pattern of GSTs in response to hypoxia stress, which induces cell death, we investigated the expression of GSTs in response to hypoxia and reoxygenation in oriental river prawn, Macrobrachium nipponense. Full-length cDNAs of two δ class GSTs were cloned from the hepatopancreas, and named MnGST-1 and MnGST-2 based on the established GST nomenclature system. Expression profiles of both GSTs in various tissues were different under acute and chronic experimental hypoxia stress conditions, suggesting that both respond strongly to hypoxia-induced oxidative stress. However, the intensity of responses to hypoxia and reoxygenation were different in different tissues. During acute hypoxia stress, MnGST-1 responds earlier than MnGST-2 in the hepatopancreas and gill, but more slowly in muscle. By contrast, during chronic hypoxia stress, MnGST-2 plays a more important role in the hepatopancreas and gill than MnGST-1.

Transcriptome Analysis Provides Insights Into the Adaptive Responses to Hypoxia of a Schizothoracine Fish (Gymnocypris eckloni)

The schizothoracine fish endemic to the Qinghai-Tibetan Plateau are comparatively well adapted to aquatic environments with low oxygen partial pressures. However, few studies have used transcriptomic profiling to investigate the adaptive responses of schizothoracine fish tissues to hypoxic stress. This study compared the transcriptomes of Gymnocypris eckloni subjected to 72 h of hypoxia (Dissolved oxygen, DO = 3.0 ± 0.1 mg/L) to those of G. eckloni under normoxia (DO = 8.4 ± 0.1 mg/L). To identify the potential genes and pathways activated in response to hypoxic stress, we collected muscle, liver, brain, heart, and blood samples from normoxic and hypoxic fish for RNA-Seq analysis. We annotated 337,481 gene fragments. Of these, 462 were differentially expressed in the hypoxic fish as compared to the normoxic fish. Under hypoxia, the transcriptomic profiles of the tissues differed, with muscle the most strongly affected by hypoxia. Our data indicated that G. eckloni underwent adaptive changes in gene expression in response to hypoxia. Several strategies used by G. eckloni to cope with hypoxia were similar to those used by other fish, including a switch from aerobic oxidation to anaerobic glycolysis and the suppression of major energy-requiring processes. However, G. eckloni used an additional distinct strategy to survive hypoxic environments: a strengthening of the antioxidant system and minimization of ischemic injury. Here, we identified several pathways and related genes involved in the hypoxic response of the schizothoracine fish. This study provides insights into the mechanisms used by schizothoracine fish to adapt to hypoxic environments.

Molecular characterization and expression of suppressor of cytokine signaling (SOCS) 1, 2 and 3 under acute hypoxia and reoxygenation in pufferfish, Takifugu fasciatus

Hypoxia seriously affects the innate immune system of fish. However, the roles of suppressor of cytokine signaling (SOCS), pivotal anti-inflammatory genes, in response to hypoxia/reoxygenation remain largely unexplored. The primary objective of this study was to elucidate the function of SOCS genes under acute hypoxia and reoxygenation in pufferfish (Takifugu fasciatus). In the present study, SOCS1, 2 and 3 were identified in T. fasciatus referred to as TfSOCS1, 2 and 3. Then, qRT-PCR and western blot analysis were employed to assess their expressions at both the mRNA and protein levels. Tissue distribution demonstrated that the three SOCS genes were predominantly distributed in gill, brain and liver. Under hypoxia challenge (1.63 ± 0.2 mg/L DO for 2, 4, 6 and 8 h), the expressions of TfSOCS1 and 3 in brain and liver at the mRNA and protein levels were significantly decreased, while their expressions showed an opposite trend in gill. Different from the expressions of TfSOCS1 and 3, the expression of TfSOCS2 was inhibited in gill, along with its increased expression in brain and liver. After normoxic recovery (7.0 ± 0.3 mg/L of DO for 4 and 12 h), most of TfSOCS genes were significantly altered at R4 (reoxygenation for 4 h) and returned to the normal level at R12 (reoxygenation for 12 h). SOCS genes played vital roles in response to hypoxia/reoxygenation challenge. Our findings greatly strengthened the relation between innate immune and hypoxia stress in T. fasciatus.

Effects of Oxygen Availability on Oxidative Stress Biomarkers in the Mediterranean Mussel Mytilus galloprovincialis

In aquatic environments, hypoxia and oxygen-deficient areas are increasing worldwide. Transitions in oxygen levels can influence the production of reactive oxygen species (ROS), eventually leading to oxidative stress. The transcriptional response of oxidative stress biomarkers was evaluated by qPCR in gill tissue from Mytilus galloprovincialis experimentally subjected to 48-h air exposure followed by 48-h re-oxygenation, as compared to normoxic control mussels. Superoxide dismutases (CuZnsod and Mnsod), catalase (cat), and glutathione S-transferase (gst) were over-expressed early after 8-h air exposure and returned to normoxic levels during re-oxygenation. Moreover, the mRNAs and protein expression patterns of heat shock proteins (HSP70 and HSP90) and metallothioneins (MT-10 and MT-20) were modulated by oxygen availability with increased levels during re-oxygenation suggesting the participation of these cytoprotective mechanisms in the physiological oxidative stress response when oxygen concentration was restored. Overall, the observed modulation of the oxidative stress-related and general stress genes indicates that M. galloprovincialis responds to changes in oxygen availability enhancing the antioxidant potential under low oxygen conditions for dealing with the oxidative burst during future re-oxygenation. The present investigation brings further insights in understanding how intertidal molluscs cope with short-term oxygen variations and gives useful biomarkers for environmental monitoring of hypoxic areas that are predicted to occur in the next future.

Dynamic mRNA and miRNA expression analysis in response to hypoxia and reoxygenation in the blunt snout bream (Megalobrama amblycephala)

Adaptation to hypoxia is a complex process involving various pathways and regulation mechanisms. A better understanding of the genetic influence on these mechanisms could permit selection for hypoxia-sensitive fish. To aid this understanding, an integrated analysis of miRNA and mRNA expression was performed in Megalobrama amblycephala under four acute hypoxia and reoxygenation stages. A number of significantly differentially-expressed miRNAs and genes associated with oxidative stress were identified, and their functional characteristics were revealed by GO function and KEGG pathway analysis. They were found to be involved in HIF-1 pathways known to affect energy metabolism and apoptosis. MiRNA-mRNA interaction pairs were detected from comparison of expression between the four different stages. The function annotation results also showed that many miRNA-mRNA interaction pairs were likely to be involved in regulating hypoxia stress. As a unique resource for gene expression and regulation during hypoxia and reoxygenation, this study could provide a starting point for further studies to better understand the genetic background of hypoxia stress.

Current Trends and Research Challenges Regarding "Preparation for Oxidative Stress"

Survival under stress, such as exposure to hypoxia, anoxia, freezing, dehydration, air exposure of water breathing organisms, and estivation, is commonly associated to enhanced endogenous antioxidants, a phenomenon coined "preparation for oxidative stress" (POS). The regulation of free radical metabolism seems to be crucial under these selective pressures, since this response is widespread among animals. A hypothesis of how POS works at the molecular level was recently proposed and relies on two main processes: increased reactive species production under hypoxia, and activation of redox-sensitive transcription factors and signaling pathways, increasing the expression of antioxidants. The present paper brings together the current knowledge on POS and considers its future directions. Data indicate the presence of POS in 83 animal species (71.6% among investigated species), distributed in eight animal phyla. Three main research challenges on POS are presented: (i) to identify the molecular mechanism(s) that mediate/induce POS, (ii) to identify the evolutionary origins of POS in animals, and (iii) to determine the presence of POS in natural environments. We firstly discuss the need of evidence for increased RS production in hypoxic conditions that underlie the POS response. Secondly, we discuss the phylogenetic origins of POS back 700 million years, by identifying POS-positive responses in cnidarians. Finally, we present the first reports of the POS adaptation strategy in the wild. The investigation of these research trends and challenges may prove useful to understand the evolution of animal redox adaptations and how they adapt to increasing stressful environments on Earth.

Identification of HIF-1 signaling pathway in Pelteobagrus vachelli using RNA-Seq: effects of acute hypoxia and reoxygenation on oxygen sensors, respiratory metabolism, and hematology indices

Oxygen is a vital element in aquatic environments. The concentration of oxygen to which aquatic organisms are exposed is influenced by salinity, water temperature, weather, and surface water runoff. Hypoxia has a serious effect on fish populations, and can lead to the loss of habitat and die-offs. Therefore, in the present study we used next-generation sequencing technology to characterize the transcriptomes of Pelteobagrus vachelli and identified 70 candidate genes in the HIF-1 signaling pathway that are important for the hypoxic response in all metazoan species. For the first time, the present study reported the effects of acute hypoxia and reoxygenation on oxygen sensors, respiratory metabolism, and hematology indices in P. vachelli. The predicted physiological adjustments show that P. vachelli's blood oxygen-carrying capacity was increased through increased RBC, HB, and SI after hypoxia exposure. Glycolysis-related enzyme activities (PFK, HK, and PK) and LDH in the brain and liver also increased, indicating a rise in anaerobic metabolism. The observed reduction in oxidative enzyme level (CS) in the liver during hypoxia suggests a concomitant depression in aerobic metabolism. There were significant increases in oxygen sensor mRNA expression and HIF-1α protein expression during hypoxia and reoxygenation exposure, suggesting that the HIF-1 signaling pathway was activated in the liver and brain of P. vachelli in response to acute hypoxia and reoxygenation. Our findings suggest that oxygen sensors (e.g., HIF-1α) of P. vachelli are potentially useful biomarkers of environmental hypoxic exposure. These data contribute to a better understanding of the molecular mechanisms of the hypoxia signaling pathway in fish under hypoxia and reoxygenation.

Abiotic Stress Responses and Microbe-Mediated Mitigation in Plants: The Omics Strategies

Abiotic stresses are the foremost limiting factors for agricultural productivity. Crop plants need to cope up adverse external pressure created by environmental and edaphic conditions with their intrinsic biological mechanisms, failing which their growth, development, and productivity suffer. Microorganisms, the most natural inhabitants of diverse environments exhibit enormous metabolic capabilities to mitigate abiotic stresses. Since microbial interactions with plants are an integral part of the living ecosystem, they are believed to be the natural partners that modulate local and systemic mechanisms in plants to offer defense under adverse external conditions. Plant-microbe interactions comprise complex mechanisms within the plant cellular system. Biochemical, molecular and physiological studies are paving the way in understanding the complex but integrated cellular processes. Under the continuous pressure of increasing climatic alterations, it now becomes more imperative to define and interpret plant-microbe relationships in terms of protection against abiotic stresses. At the same time, it also becomes essential to generate deeper insights into the stress-mitigating mechanisms in crop plants for their translation in higher productivity. Multi-omics approaches comprising genomics, transcriptomics, proteomics, metabolomics and phenomics integrate studies on the interaction of plants with microbes and their external environment and generate multi-layered information that can answer what is happening in real-time within the cells. Integration, analysis and decipherization of the big-data can lead to a massive outcome that has significant chance for implementation in the fields. This review summarizes abiotic stresses responses in plants in-terms of biochemical and molecular mechanisms followed by the microbe-mediated stress mitigation phenomenon. We describe the role of multi-omics approaches in generating multi-pronged information to provide a better understanding of plant-microbe interactions that modulate cellular mechanisms in plants under extreme external conditions and help to optimize abiotic stresses. Vigilant amalgamation of these high-throughput approaches supports a higher level of knowledge generation about root-level mechanisms involved in the alleviation of abiotic stresses in organisms.

Physiological responses and changes in gene expression in the large yellow croaker Larimichthys crocea following exposure to hypoxia

Organisms at all levels of evolutionary complexity react to hypoxic stress. To clarify the effects of acute hypoxia on physiological and biochemical responses of Larimichthys crocea, we measured the activity levels of the antioxidant enzymes superoxide dismutase and catalase, hemoglobin concentration, functional indices of the liver (aspartate transaminase, alanine transaminase), heart (phosphocreatine kinase), and immune system (alkaline phosphatase), as well as mRNA expression levels of the immunity-related genes Hsp70 and HIF-1α at different time points of hypoxic. In addition, liver, gill, and kidney samples were histologically analyzed. We found that hemoglobin concentration and all enzyme activities increased during hypoxia, although these effects were transient and most indices returned to basal levels thereafter. The extent of the increase in the parameter values was inversely proportional to the dissolved oxygen content. Hsp70 and HIF-1α mRNA expression levels increased significantly in the blood, liver, gills, and kidneys following exposure to hypoxia, which may play an important role in protecting fish against oxidative damage. However, we found histological evidence of hypoxia-induced injuries to the gills, liver, and kidneys, which are involved in breathing, detoxification, and osmotic balance maintenance, respectively. Thus, despite the upregulation of defensive mechanisms, acute hypoxia still caused irreversible damage of organs. In conclusion, we observed that, in response to acute hypoxic stress, L. crocea enhances immune defensive function and antioxidant capacity. A better understanding of the regulation of the molecular anti-hypoxia mechanisms can help speeding up the selective breeding of hypoxia-tolerant L. crocea.