Investigation of Proteus vulgaris and Elizabethkingia meningoseptica invasion on muscle oxidative stress and autophagy in Chinese soft-shelled turtle (Pelodiscus sinensis).

Muscle is an important structural tissue in aquatic animals and it is susceptible to bacterial and fungal infection, which could affect flesh quality and health. In this study, Chinese soft-shelled turtles were artificially infected with two pathogens, Proteus vulgaris and Elizabethkingia meningoseptica and the effects on muscle nutritional characteristics, oxidative stress and autophagy were assayed. Upon infection, the muscle nutritional composition and muscle fiber structure were notably influenced. Meanwhile, the mRNA expression of Nrf2 was down-regulated and Keap1 up-regulated, thus resulting in a decrease in antioxidant capacity and oxidative stress. However, with N-acetylcysteine treatment, the level of oxidative stress was decreased, accompanied by significant increases in antioxidant enzyme activities and the mRNA levels of SOD, CAT, GSTCD, and GSTO1. Interestingly, there was a significant increase in autophagy in the muscle tissue after the pathogen infection, but this increase could be reduced by N-acetylcysteine treatment. Our findings suggest that muscle nutritional characteristics were dramatically changed after pathogen infection, and oxidative stress and autophagy were induced by pathogen infection. However, N-acetylcysteine treatment could compromise the process perhaps by decreasing the ROS level and regulating Nrf2-antioxidant signaling pathways.

Abrupt salinity stress induces oxidative stress via the Nrf2-Keap1 signaling pathway in large yellow croaker Pseudosciaena crocea.

The aim of the present study was to evaluate the effects of abrupt salinity stress (12, 26 (control), and 40) on lipid peroxidation, activities and mRNA levels of antioxidant enzymes (Cu/Zn-SOD, CAT, GPx, and GR), and gene expression of the Nrf2-Keap1 signaling molecules at different times (6, 12, 24, and 48 h) in the liver of large yellow croaker Pseudosciaena crocea. The results showed that lipid peroxidation was sharply reduced at 6 h and increased at 12 h before returning to control levels in the hypo-salinity group. Similarly, lipid peroxidation was significantly decreased at 6 h followed by a sharp increase towards the end of the exposure in the hyper-salinity group. Negative relationships between lipid peroxidation and antioxidant enzyme activities and positive relationships between activities and gene expression of antioxidant enzymes were observed, suggesting that the changes at molecular levels and enzyme activity levels may provide protective roles against damage from salinity stress. Obtained results also showed a coordinated transcriptional regulation of antioxidant genes, suggesting that Nrf2 is required for regulating these genes. Furthermore, there was a positive relationship between the mRNA levels of Nrf2 and Keap1, indicating that Keap1 plays an important role in switching off the Nrf2 response. In conclusion, this is the first study to elucidate effects of salinity stress on antioxidant responses in large yellow croaker through the Keap1-Nrf2 pathway.

Molecular characterization and expression analysis of AMPK α subunit isoform genes from Scophthalmus maximus responding to salinity stress.

AMP-activated protein kinase (AMPK) is a highly conserved and multi-functional protein kinase that plays important roles in both intracellular energy balance and cellular stress response. In the present study, molecular characterization, tissue distribution and gene expression levels of the AMPK α1 and α2 genes from turbot (Scophthalmus maximus) under salinity stress are described. The complete coding regions of the AMPK α1 and α2 genes were isolated from turbot through degenerate primers in combination with RACE using muscle cDNA. The complete coding regions of AMPK α1 (1722 bp) and α2 (1674 bp) encoded 573 and 557 amino acids peptides, respectively. Multiple alignments, structural analysis and phylogenetic tree construction indicated that S. maximus AMPK α1 and α2 shared a high amino acid identity with other species, especially fish. AMPK α1 and α2 genes could be detected in all tested tissues, indicating that they are constitutively expressed. Salinity challenges significantly altered the gene expression levels of AMPK α1 and α2 mRNA in a salinity- and time-dependent manners in S. maximus gill tissues, suggesting that AMPK α1 and α2 played important roles in mediating the salinity stress in S. maximus. The expression levels of AMPK α1 and α2 mRNA were a positive correlation with gill Na+, K+-ATPase activities. These findings will aid our understanding of the molecular mechanism of juvenile turbot in response to environmental salinity changes.