Oxygen is our friend and our enemy. Without it there would be no life on earth, but the damaging effects of oxygen lead to ageing and disease. Kristin O'Brien, from the University of Alaska, Fairbanks, explains that oxidative damage can increase when temperatures drop and this is a risk for cold-blooded species such as fish. But no one knew how much of a risk. ‘Although several studies have measured oxidative stress during cold acclimation of fishes, the results have been equivocal,’ says O'Brien. Curious to find out how sticklebacks respond to cold acclimation, O'Brien and her colleagues Aaron Kammer and Julieanna Orczewska measured the levels of oxidative damage and antioxidants including superoxide dismutase (SOD) – which detoxifies damaging superoxide – in warm and cold threespine sticklebacks ().
The team looked for oxidative damage in liver, oxidative and glycolytic muscles, and initially found damaged proteins in the cold fish's livers; however, the damage levels began to decrease after 4 weeks and there was no evidence of oxidative damage in either muscle type. The team also found an increase in the amount of the antioxidant glutathione in liver within 3 days of dropping the fish's temperature. When they looked at the activity of SOD at 14°C, they found it had increased on the second day of cooling in both muscle types and by day 3 in the fish's liver. However, when the team analysed SOD's activity at the fish's physiological temperature, They found it only rose in the oxidative muscles of fish that had been cooled for 9 weeks and remained constant in the cold fish's liver and glycolytic muscle. O'Brien and her colleagues suspect that the increase in SOD activity is due to modification of the protein after transcription, as the levels of SOD enzyme activity increase prior to an increase in mRNA levels.
O'Brien says, ‘Our results demonstrate that oxidative stress is tissue specific and transient during cold acclimation of sticklebacks.’ She also suggests that SOD activity levels may not rise in all tissues to combat elevated levels of superoxide production in cold conditions, but may rise instead to counteract the decreased catalytic rate of SOD in the cold.
