Catalase activity is heterogeneous among tissues in the Weddell seal, and consistent with patterns of tissue perfusion during diving
Authors: Skoler Eliza , Batten Annabelle , Hindle Allyson 
Published: June 2021

Hypoxia/ischemia that occurs when tissue blood flow is compromised, and subsequent reoxygenation/reperfusion when it is then recovered, is expected to deliver an oxidative stress insult to cells. However, many species are naturally tolerant of hypoxic and ischemic conditions. Weddell seals routinely restrict blood flow to certain peripheral tissues to conserve oxygen during extended dives, yet their tissues do not demonstrate markers of damage from oxidative stress. Understanding how Weddell seals cope with scenarios that generate oxidative stress in terrestrial mammals has the potential to inform human therapies and suggest mechanisms of protection against ischemic and hypoxic injury. Seals have been shown to have higher tissue antioxidant activities than terrestrial mammals generally, however degree of ischemia varies by tissue, and the degree to which antioxidant protective mechanisms track this variation is unknown. This study hypothesized that if the antioxidant catalase is a component of protection against ischemia/reperfusion in diving seals, that catalase activity would correlate with degree of hypoperfusion expected in different tissues. Catalase activity was measured in the right ventricle, cerebral cortex, and kidney homogenates of five seal adults, five seal pups, and compared to similar measurements in six adult sheep. Protein abundance was measured in the same tissues by western blot, and mRNA expression was measured with qPCR using species‐specific primers. In both species, catalase activity was highest in kidney and lowest in brain. However, kidney catalase activity was 71% higher in the diving seal than in terrestrial sheep (p = 0.00003), consistent with the observation that the seal kidney experiences the greatest degree of blood flow reduction during extended diving. Blood flow is only marginally reduced in the diving seal's heart, but maintained in the brain during submergence. As predicted, catalase activity in the heart was also moderately higher in seals than in sheep (33%, p = 0.04), whereas brain catalase activity was comparable between species (p = 0.8). Western immunoblot and qPCR results supported the tissue‐specific activity differences, demonstrating that catalase protein and mRNA levels were highest in kidney and lowest in brain. These results are consistent with the interpretation that tissues most exposed to repetitive hypoxemia/reoxygenation in seals do have proportionally higher expression of catalase, resulting in higher antioxidant activity. However protein and transcript levels did not align with differences in enzyme activity between seals and sheep, suggesting that further research is required to elucidate whether Weddell seal catalase is functionally different than terrestrial species.Support or Funding InformationFunding by the National Science Foundation and the American Physiological Society's Undergraduate Summer Research Fellowship program.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.