Intracellular antioxidant enzymes are not globally upregulated during hibernation in the major oxidative tissues of the 13-lined ground squirrel Spermophilus tridecemlineatus

Hibernating mammals exhibit oxidative stress resistance in brain, liver and other tissues. In many animals, cellular oxidative stress resistance is associated with enhanced expression of intracellular antioxidant enzymes. Intracellular antioxidant capacity may be upregulated during hibernation to protect against oxidative damage associated with the ischemia-reperfusion that occurs during transitions between torpor and arousal. We tested the hypothesis that the 13-lined ground squirrel (Spermophilus tridecemlineatus), upregulates intracellular antioxidant enzymes in major oxidative tissues during hibernation. The two major intracellular isoforms of superoxide dismutase (MnSOD and CuZnSOD), which catalyze the first step in superoxide detoxification, were quantified in heart, brain and liver tissue using immunodetection and an in-gel activity assay. However, no differences in SOD protein expression or activity were found between active and hibernating squirrels. Measurements of glutathione peroxidase and glutathione reductase, which catalyze hydrogen peroxide removal, were not broadly upregulated during hibernation. The activity of catalase, which catalyzes an alternative hydrogen peroxide detoxification pathway, was higher in heart and brain of torpid squirrels, but lower in liver. Taken together, these data do not support the hypothesis that hibernation is associated with enhanced oxidative stress resistance due to an upregulation of intracellular antioxidant enzymes in the major oxidative tissues.