Heat shock protein 70 gene expression and stress response of red-spotted (Epinephelus akaara) and hybrid (E. akaara female × E. lanceolatus male) groupers to heat and cold shock exposure

Physiological responses of hybrid grouper (Epinephelus fuscoguttatus X Epinephelus lanceolatus) to temperature fluctuation stress revealed by LCMS/MS-based mucus and sera metabolomics

Aquaculture, which involves the cultivation of aquatic animals and plants, is recognised to be an effective and vital resource-efficient food production system for supplying affordable protein to humans. Hybrid grouper (Epinephelus fuscoguttatus x Epinephelus lanceolatus) is a marine carnivorous teleost that has a high economic importance in the marine aquaculture industry particularly in countries in the Asian region. However, the vulnerability of juvenile hybrid grouper to temperature fluctuations stemming from the acceleration of climate change is regarded as one of significant threats to their market supply and a major concern for the aquaculture industry. In the present study, LCMS/MS-based mucus and sera metabolomics were used to investigate the physiological responses of juvenile hybrid grouper via their behavioural response towards temperature fluctuation stress that could be translated as indicators for either resilience or susceptibility to the stressors. Susceptible fish exhibited pronounced behavioural responses, including cessation of feeding and erratic swimming. In contrast, resilient fish displayed relatively stable behaviour, comparable to control fish, with reduced feeding as a primary deviation. A total of 36 mucus metabolites (VIP > 1) were profiled in OPLSDA in juvenile hybrid grouper subjected to temperature fluctuation stress. Among these, 20 and 16 metabolites were significantly altered (Student's t-test, p < 0.05) in susceptible (MSG) and resilient (MRG) fish in comparison to the control (CG), respectively. Although OPLSDA did not reveal a clear separation between the two groups, 4 metabolites namely glycerophosphocholine, N-acetylgalactosamine, N-acetylglucosamine, and pantothenic acid differed significantly between them. In sera, 54 metabolites (VIP > 1) were profiled, with 38 and 26 significantly altered in the susceptible (SSG) and resilient (SRG) groups, respectively. Comparative analysis between significant and resilient groups resulted in the nomination of hypoxanthine, guanosine, guanine, methionine, DL-malic acid, and glucose as potential biomarkers for susceptibility in juvenile hybrid grouper. Pathway analysis of these metabolite markers revealed that temperature stress mainly affected purine metabolism, TCA cycle, cysteine and methionine metabolism, and pyruvate metabolism. Overall, the findings of this study provide insights into the physiological regulation of juvenile hybrid grouper that are susceptible to temperature changes through their behavioural response, as well as a framework for future research.

Heat-shock protein 70 reduces apoptosis in the gills and hepatopancreas of Marsupenaeus japonicus under low-temperature stress

The heat shock response (HSR) has important functions in a cell's reaction to stresses. The HSR is regulated and effected by heat shock proteins (HSPs) and heat shock factors (HSFs). Herein, the full-length cDNA of Marsupenaeus japonicus heat shock protein 70 (MjHSP70) was isolated and sequenced. The MjHSP70 cDNA comprised 2346 bp with an open reading frame of 1959 bp, encoding a protein of 653 amino acids. Both MjHSF1 and MjHSP70 are widely expressed across tissues. In response to low temperature stress, MjHSF1 and MjHSP70 expression levels were significantly upregulated in the gill and hepatopancreas. After RNA interference-mediated knockdown of MjHSP70, the mortality rate of M. japonicus increased significantly under low temperature stress, apoptotic genes, e.g., Mjcaspase3 and Mjbcl2, showed significantly upregulated expression, and the apoptotic cell count also increased. Additionally, dual luciferase assays showed that MjHSF1 activated MjHSP70 transcription, and MjHSP70 expression was downregulated after MjHSF1 silencing. The results of glutathione-S-transferase GST pull-down assays indicated that MjHSP70 interacted with MjHSF1's DNA binding domain. Our findings suggested that the MjHSF1-MjHSP70 axis exerts a vital function in M. japonicus' immune response to cold stress.

The regulation of ovarian degeneration in Pampus argenteus by heat shock protein genes under low-temperature stress

Temperature is a crucial environmental factor that significantly impacts the growth, development, metabolism, and physiological functions of fish. To study the effects of low-temperature on the gonadal development of silver pomfret (Pampus argenteus), a cold period by gradually lowering the water temperature from 18°C to 9°C was simulated. The results showed that hsp70, hsp90a, and hsp90b were widely expressed in the tissues of P. argenteus, with hsp70 primarily expressed in the pituitary, hsp90a and hsp90b mainly expressed in the lateral. The hsps were involved in the development process of P. argenteus from 1 to 27 days post-hatching (dph). The expression levels of hsp70 and hsp90b were highest at 17 dph, while the levels of hsp90a were at 25 dph. Under the condition of 9°C, regressed oocyte were observed in the ovaries, the oocyte diameter significantly decreased, and the ovaries degenerated 100% after low-temperature stress. The expression levels of hsps in the ovaries were significantly higher than in the control group, while the expression levels in the testes were significantly lower than in the control group. Taken together, hsps may regulate the ovarian degeneration under low-temperature stress. Male fish rapidly completed meiosis and maintained the testes in the prophase of meiosis to resist the low-temperature stress.

Tissue Accumulation, Cytotoxicity, Oxidative Stress, and Immunotoxicity in African Catfish, Clarias gariepinus Exposed to Sublethal Concentrations of Hexavalent Chromium

Hexavalent chromium (Cr6+) is one of the stable oxidation states of chromium that has been reported to elicit various toxic effects in aquatic organisms. However, the mechanisms of Cr6+ toxicity are still poorly understood. Thus, the present study investigated the tissue accumulation, cytotoxic, oxidative stress, and immunotoxic effects of Cr6+ in juvenile Clarias gariepinus. The fish were exposed to waterborne Cr6+ concentrations (0, 0.42, 0.84, and 1.68 mg/L) for 28 days, after which they were sacrificed and various organs were harvested for the determination of Cr6+ levels. Other parameters that were indicators of oxidative stress, cytotoxicity, and immunotoxicity were measured. Cr6+ accumulated more in the kidney and liver of the exposed fish, especially at the highest concentration. The levels of lipid peroxidation and DNA fragmentation increased significantly in the exposed fish. The activities of superoxide dismutase and lactate dehydrogenase increased significantly in exposed fish compared to the control. The total white blood cells, lymphocytes, and neutrophils counts were significantly higher in the exposed fish compared to the control fish. The respiratory burst activity decreased significantly in the exposed fish while the myeloperoxidase content did not differ significantly. There were upregulations of TNF-α and HSP 70 while CYP II and MHC 2 were downregulated in the exposed fish. Also, exposure to Cr6+ resulted in various histopathological alterations in the architecture of the head kidney. The results indicate concentration-dependent toxic effects of Cr6+ in C. gariepinus. The study reveals the potentials of Cr6+ to accumulate in the different tissues of fish and caused cytotoxic, oxidative stress, and immunotoxic effects in the exposed fish.

Transcriptomic and Phenotypic Analysis of CRISPR/Cas9-Mediated gluk2 Knockout in Zebrafish

As a subtype of kainite receptors (KARs), GluK2 plays a role in the perception of cold in the periphery sensory neuron. However, the molecular mechanism for gluk2 on the cold stress in fish has not been reported. In this article, real-time PCR assays showed that gluk2 was highly expressed in the brain and eyes of adult zebrafish. To study the functions of gluk2, gene knockout was carried out using the CRISPR/Cas9 system. According to RNA-seq analysis, we selected the differentially expressed genes (DEGs) that had significant differences in at least three tissues of the liver, gill, intestine, skin, brain, and eyes. Gene Ontology (GO) enrichment analysis revealed that cry1ba, cry2, per1b, per2, hsp70.1, hsp70.2, hsp70l, hsp90aa1.1, hsp90aa1.2, hspb1, trpv1, slc27a1b, park2, ucp3, and METRNL were significantly enriched in the ‘Response to temperature stimulus’ pathway. Through behavioral phenotyping assay, the gluk2^−/− larval mutant displayed obvious deficiency in cold stress. Furthermore, TUNEL (TdT-mediated dUTP Nick-End Labeling) staining proved that the gill apoptosis of gluk2^−/− mutant was increased approximately 60 times compared with the wild-type after gradient cooling to 8 °C for 15 h. Overall, our data suggested that gluk2 was necessary for cold tolerance in zebrafish.

Cold Stress Induced Liver Injury of Mice through Activated NLRP3/Caspase-1/GSDMD Pyroptosis Signaling Pathway

The body needs to generate heat to ensure basic life activities when exposed to cold temperatures. The liver, as the largest glycogen storage organ in the body and main heat-producing organ at rest, may play a role in chronic cold exposure. Recent studies suggested that pyroptosis plays a crucial role in liver diseases. However, the role of pyroptosis in cold stress-induced liver injury is not clear. Hence, in this study, we attempted to investigate the effects of chronic cold exposure on liver function, apoptosis, oxidative stress and inflammation in mice by establishing a mouse model of chronic cold exposure, and to investigate whether pyroptosis pathways are involved in the process of chronic cold exposure. In vivo, our results show that inflammatory cell infiltration and other pathological changes in liver cells and the activity of liver enzyme evidently increased in the serum and liver of cold-exposed mice, suggesting cold stress may result in liver injury. Remarkably, increased expression of heat shock protein 70 (HSP70) and HSP90 proteins proved the cold stress model is successfully constructed. Then, elevated levels of apoptosis, inflammation, oxidative stress and pyroptosis related proteins and mRNAs, such as cysteinyl aspartate specific proteinase-3 (Caspase-3), inducible nitric oxide synthase (iNOS), nuclear factor erythroid2-related factor 2 (Nrf2) and gasdermins D (GSDMD), confirmed that cold exposure activated apoptosis, oxidative stress and pyroptosis, and released inflammation cytokines. Meanwhile, in vitro, we got similar results as in vivo. Further, adding an NLR family pyrin domain containing 3 (NLRP3) inhibitors found that suppression expression of NLRP3 results in the essential proteins of pyroptosis and antioxidant evidently reduced, and adding GSDMD inhibitor found that suppression expression of GSDMD accompanies with the level of Nrf2 and heme oxygenase-1 (HO-1) obviously reduced. In summary, these findings provide a new understanding of the underlying mechanisms of the cold stress response, which can inform the development of new strategies to combat the effects of hypothermia.