Hypoxia exerts oxidative stress and changes in expression of antioxidant enzyme genes in gills of Mytilus galloprovincialis (Lamarck, 1819)

ABSTRACT

Bivalve molluscs are widespread in coastal environments, where they are subjected to a wide range of environmental fluctuations, which can represent a significant impact to their antioxidant status. Hypoxia is a global problem affecting the world’s shallow waters, which is forecast to increase in coastal areas due to anthropogenic pressure and global warming. In this work, the effects of 24 h exposure to hypoxia (0.2 mg O₂ l⁻¹) on antioxidant parameters of Mytilus galloprovincialis were investigated. Functional parameters of gill samples (the number of dead cells and intracellular reactive oxygen species concentration) were measured by flow cytometry, and the expression level of antioxidant enzyme genes (CAT, GST, SOD) as well as NADH dehydrogenase subunit 2 were analysed using transcriptome analysis. Gills responded to oxygen depletion by an increased total number of intracellular reactive oxygen species, which was accompanied with high levels of mortality of cells (10 times higher compared with control). Significant increases of Mn-superoxide dismutase, glutathione S-transferase and NADH dehydrogenase subunit 2 gene expression levels were observed. Hypoxia did not cause changes in the expression of CAT. The results indicate an overall shift in antioxidant parameters in gill tissue that may represent a certain level of oxidative stress in mussels and decreased capacity of the antioxidant system to maintain redox homeostasis after exposure to hypoxia.

KEYWORDS:

• Hypoxia
• oxidative stress
• haemocytes
• gills
• antioxidant gene expression
• Mytilus galloprovincialis
• NADH2

Acknowledgements

The effect of hypoxia on the level of mortality in gill cells was investigated according to State Assignment (state registration number N 121041400077-1). RNA extraction, cDNA preparation and sequencing were funded by Ministry of Education and Science of the Russian Federation: 14.W03.31.0015. The high-throughput sequencing was performed at IC&G Center of Genomic Investigations, bioinformatic analysis of the sequenced data was funded by the State Assignment (state registration number No. 121030100028-0) and the internal grant of SSU for 2020 No. 33/06-31. The RNA-seq data analysis was performed using computational resources of the ‘Bioinformatics’ Joint Computational Center of the Institute of Cytology and Genetics SB RAS.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The study effect of hypoxia on the level of mortality in gill cells was funded by the State Assignment (state registration number N 121041400077-1). RNA extraction, cDNA preparation and sequencing were funded by Ministry of Education and Science of the Russian Federation: 14.W03.31.0015. The high-throughput sequencing was performed at IC&G Center of Genomic Investigations, bioinformatic analysis of the sequenced data was funded by the State Assignment (state registration number No. 121030100028-0) and the internal grant of SSU for 2020 No. 33/06-31. The RNA-seq data analysis performed using computational resources of the “Bioinformatics” Joint Computational Center of the Institute of Cytology and Genetics SB RAS supported by the budget project No 0324-2019-0040-C-01.