Hypoxia acts together with pollutants to decrease animal success in aquatic environments

Hypoxia is recognized as one of the most important problems for aquatic organisms. The ocean deoxygenation problem is the subject of a recent IUCN report, downloadable from https://www.iucn.org/resources/publications. Deoxygenation is not acting alone. Many anthropogenic pollutants cause oxidative stress. In recent years, measuring parameters associated with oxidative stress has become one of the favourite areas among aquatic toxicologists. Thus, one would have expected that investigations about interactions between hypoxia and pollutants causing oxidative stress would be common. However, this is not so, even though the interactions may cause increased mortality either directly or by affecting energy metabolism, or  decreased reproductive success either directly or by decreasing energy available for reproduction.

The reason for this is that hypoxia responses normally take place in or are initiated by reducing environment – hypoxia in absence of pollutants is such an environment. Already in 2004 we published a paper (Nikinmaa et al., Journal of Cell Science 117, 3201-3206) concluding: “As redox reactions play a pronounced role in the stability, DNA binding and phosphorylation of HIF-1a protein in salmonid cells, it is likely that environmental disturbances involving oxidative stress, such as metal or organic pollutant contamination and increased UV radiation, may influence HIF-1a protein function and consequent gene expression.” Already then the importance of   HIF (Hypoxia-Inducible Protein) was clear, but its importance in regulating hypoxia responses was emphasized by the Nobel prize, which was given to scientists (Semenza, Ratcliffe and Kaelin), who have clarified its regulation. We showed in 2004 (Vuori et al. Aquatic Toxicology 68, 301-313) that the reproductive disturbance   of Baltic salmon, which may be associated with oxidative stress, is also associated with HIF dysfunction. If hypoxic conditions occur together with oxidative stress, the combination may be fatal, because the hypoxia response pathway is disturbed.

While the above scenario is hypothetical, it clearly shows the possibility of hypoxia-oxidative stress interactions, and the reason and rationale for studies investigating them. As a third component for such studies is temperature increase, occurring together with the spreading of hypoxic areas.