Duplicated connective tissue growth factor genes in hypoxia-sensitive blunt snout bream Megalobrama amblycephala and their in vivo expression

Aspirin exposure coupled with hypoxia interferes energy metabolism, antioxidant and autophagic processes and causes liver injury in estuarine goby Mugilogobius chulae

Toxicity assessments of pollutants often overlook the impact of environmental factors like hypoxia, which can alter chemical toxicity with unexpected consequences. In this study, Mugilogobius chulae, an estuarine fish, was used to investigate the effects of hypoxia (H), aspirin (ASA), and their combination (H_ASA) exposure over 24, 72, and 168 h. We employed RNA-seq analysis, expression of key gene expression profiling, enzymatic activity assays, and histopathological and ultrastructural examinations of liver tissue to explore the effects and mechanisms of ASA-coupled hypoxia exposure in fish. Results showed that glycolysis was inhibited, and lipolysis was enhanced in ASA/H_ASA groups. The PPAR signaling pathway was activated, increasing fatty acid β-oxidation and lipophagy to mitigate energy crisis. Both ASA and H_ASA exposures induced p53 expression and inhibited the TOR pathway to combat environmental stress. However, a greater energy demand and heightened sensitivity to ASA were observed in H_ASA compared to ASA exposure. Disruptions in energy and detoxification pathways led to increased stress responses, including enhanced antioxidant activities, autophagy, and apoptotic events, as observed in organelle structures. Overall, sub-chronic H_ASA exposure caused liver injury in M. chulae by affecting energy metabolism, antioxidant regulation, and autophagy processes. This study highlights the influence of hypoxia on ASA toxicity in fish, providing valuable insights for ecological risk assessment of NSAIDs.

Efficacy of quercetin in ameliorating hypoxia-induced hematological and histopathological alterations in rohu Labeo rohita

Hypoxia, a major issue in aquatic ecosystems, in special reference to climate change, and exacerbated by anthropogenic activities. It is causing slow growth, disease outbreaks, and mortality in finfish and shellfish. Therefore, adaptation to lowering oxygen levels through supplementation of herbs or their extracts in diets is imperative. In this study, hypoxia was simulated in controlled conditions with quercetin-enriched diets. Quercetin is a plant pigment (flavonol) possessing anti-oxidant property and is present in vegetables, leaves, seeds, pulses, and fruits. The experiment was conducted on rohu Labeo rohita, which is most widely cultured in India. There were four treatments including T1 (Normoxia: > 5 ppm dissolved oxygen; DO2), T2 (hypoxia: 3-4 ppm DO2), T3 (hypoxia + 50 mg quercetin/kg diet), and T4 (hypoxia + 100 mg quercetin/kg diet). The study was conducted for 30 days, and water quality was measured regularly. The results revealed that the hematological parameters were negatively affected. The tissue micro-architecture illustrated the impairment through degeneration of neurons in the brain, increased pigmentation as melanosis in the kidney, increased thickness of primary lamellae in the gills, and dilatations of sinusoids in the liver in hypoxia groups, while quercetin-enriched diets improved the hematological and histomorphological parameters. The results confirm the utility of hematological and histopathological tools as biomarkers and reflect the possible threats of hypoxia on fish. In conclusion, quercetin in diets appeared to show resistance towards chronic hypoxia by restoring the structure and functions of the vital organs towards normalcy and could be recommended as a potential ameliorative agent.

Hypoxia aggravates the burden of yellowstripe goby (Mugilogobius chulae) under atorvastatin exposure

In the present study, an estuarine benthic fish, Mugilogobius chulae (M. chulae), was exposed to hypoxia, atorvastatin (ATV), a highly used and widely detected lipid-lowering drug in aquatic environment, and the combination of hypoxia and ATV for 7 days, respectively, so as to address and compare the effects of the combination of hypoxia and ATV exposure on M. chulae. The results showed that lipid metabolism in M. chulae was greatly affected: lipid synthesis was blocked and catabolism was enhanced, exhibiting that lipids content were heavily depleted. The combined exposure of hypoxia and ATV caused oxidative stress and induced massive inflammatory response in the liver of M. chulae. Signaling pathways involving in energy metabolism and redox responses regulated by key factors such as HIF, PPAR, p53 and sirt1 play important regulatory roles in hypoxia-ATV stress. Critically, we found that the response of M. chulae to ATV was more sensitive under hypoxia than normoxia. ATV exposure to aquatic non-target organisms under hypoxic conditions may make a great impact on the detoxification and energy metabolism, especially lipid metabolism, and aggravate the oxidative pressure of the exposed organisms.

Characterization and role of connective tissue growth factor gene in collagen synthesis in swim bladder of chu's croaker (Nibea coibor)

Connective tissue growth factor (Ctgf) is a matricellular protein with diverse biological function. It is regarded as a central regulator of tissue fibrosis and collagen synthesis in mammals. However, its roles in fish remain elusive. Here, a ctgf gene was cloned (NcCtgf), characterized and functionally studied in the chu's croaker (Nibea coibor). NcCtgf encoded a protein containing 346 amino acids, 38 conserved cysteine residues, 4 functional domains and a signal peptide. NcCtgf shared highest identity (99.4 %) to the Larimichthys crocea Ctgf protein. Phylogenetic tree revealed that NcCtgf clustered with the teleost Ctgfa and Ctgf of higher vertebrates, instead of teleost Ctgfb. NcCtgf was expressed with higher level in gonad, spleen, gill and swimming bladder than other tissues, and was up-regulated in swim bladder synchronously with collagen I genes by hydroxyproline and TGF-β1 treatment. NcCtgf knockdown/overexpression inhibited/promoted collagen synthesis in swim bladder cell, respectively. Notably, NcCtgf protein could be secreted to cell culture medium and up-regulated collagen I expression in swim bladder cell. These findings indicate NcCtgf plays vital roles in collagen synthesis in swim bladder of Nibea coibor, and provide basis for further understanding of ctgf evolution and exploring new approach for enhancing collagen deposition in fish products during aquaculture.

The transcriptomic responses of blunt snout bream (Megalobrama amblycephala) to acute hypoxia stress alone, and in combination with bortezomib

BACKGROUND

Blunt snout bream (Megalobrama amblycephala) is sensitive to hypoxia. A new blunt snout bream strain, "Pujiang No.2", was developed to overcome this shortcoming. As a proteasome inhibitor, bortezomib (PS-341) has been shown to affect the adaptation of cells to a hypoxic environment. In the present study, bortezomib was used to explore the hypoxia adaptation mechanism of "Pujiang No.2". We examined how acute hypoxia alone (hypoxia-treated, HN: 1.0 mg·L^- 1), and in combination with bortezomib (hypoxia-bortezomib-treated, HB: Use 1 mg bortezomib for 1 kg fish), impacted the hepatic ultrastructure and transcriptome expression compared to control fish (normoxia-treated, NN).

RESULTS

Hypoxia tolerance was significantly decreased in the bortezomib-treated group (LOE_crit, loss of equilibrium, 1.11 mg·L^- 1 and 1.32 mg·L^- 1) compared to the control group (LOE_crit, 0.73 mg·L^- 1 and 0.85 mg·L^- 1). The HB group had more severe liver injury than the HN group. Specifically, the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the HB group (52.16 U/gprot, 32 U/gprot) were significantly (p < 0.01) higher than those in the HN group (32.85 U/gprot, 21. 68 U/gprot). In addition, more severe liver damage such as vacuoles, nuclear atrophy, and nuclear lysis were observed in the HB group. RNA-seq was performed on livers from the HN, HB and NN groups. KEGG pathway analysis disclosed that many DEGs (differently expressed genes) were enriched in the HIF-1, FOXO, MAPK, PI3K-Akt and AMPK signaling pathway and their downstream.

CONCLUSION

We explored the adaptation mechanism of "Pujiang No.2" to hypoxia stress by using bortezomib, and combined with transcriptome analysis, accurately captured the genes related to hypoxia tolerance advantage.

Isolation and characterization of hypoxia inducible gene connective tissue growth factor (CTGF) in Labeo rohita

The connective tissue growth factor gene plays important role in several biological processes and also responsive to hypoxia stress in fishes. The freshwater fish, Labeo rohita, highly cultured in Indian subcontinent for food, is reported as hypoxia sensitive but annotation and sequences of nuclear genes were not available for this species so far in the public domain, except some transcripts. In this study, an attempt was made for isolation and annotation of the CTGF gene in L. rohita using information of zebrafish from the same family. The CTGF gene sequence was obtained by aligning assembled genome of L. rohita, (NCBI BioProject ID: PRJNA437789), with the CTGF protein of zebrafish. Eight overlapping sets of forward and reverse primers from aligned region were designed for amplification of around 600 bp long successive overlapping fragments of CTGF gene in L. rohita. Assembly and annotation of overlapping fragments confirmed a complete 2421 bp long CTGF gene sequence with a full coding region that comprised of five exons between 308 and 1921 positions. This annotated CTGF gene sequence was submitted to GenBank (Acc. No. KY940466). Characterization of CTGF will be an initiative in identification of hypoxia response genes in L. rohita which may further help in understanding the mechanism of hypoxia tolerability in this species.

Characterization of duplicated heme oxygenase-1 genes and their responses to hypoxic stress in blunt snout bream (Megalobrama amblycephala)

The heme oxygenase (HO)-1 is a cytoprotective enzyme that can be involved in cytoprotection against hypoxia stress. In this study, we cloned duplicated HO-1a and HO-1b cDNAs in hypoxia-sensitive blunt snout bream (Megalobrama amblycephala). HO-1a and HO-1b encode peptides with 272 amino acids and 246 amino acids, respectively, and they share a low sequence identity of 55%. HO-1a and HO-1b mRNAs were maternally deposited in the zygote, and the mRNAs decreased to the lowest levels at 8 hpf. Both mRNAs were significantly (p < 0.01) expressed from 12 hpf and fluctuated but maintained a high level after 16 hpf. Using in situ hybridization, HO-1a and HO-1b mRNAs were ubiquitously expressed in embryos at 12 hpf. At 24 and 36 hpf, HO-1b transcripts were detected in the mid- and hindbrain, respectively, whereas HO-1a was mainly transcribed in the eyes and endoderm at 24 hpf and in the brain at 36 hpf. In adult fish, HO-1a was abundantly expressed in the heart, liver, gill, kidney, spleen, and brain, while HO-1b mRNA was detected mainly in the kidney. After exposure to hypoxic stress, both HO-1a and HO-1b mRNAs were upregulated significantly in the gill and liver but downregulated significantly in the brain (p < 0.01). These findings suggest that duplicated HO genes have evolved divergently and yet play overlapping biological roles in regulating the response to hypoxia in M. amblycephala.