Role of NADP thorn -dependent isocitrate dehydrogenase from muscle tissue of Rana sylvatica in ROS defense during freeze-tolerance

The wood frog, Rana sylvatica, employs freeze tolerance as a winter survival strategy in seasonally cold environments. At subzero temperatures, up to 65-70% of total body water can freeze in extracellular spaces, halting vital functions (breathing, heartbeat) and causing ischemia that, in turn, can have numerous consequences including the generation of damaging reactive oxygen species (ROS). NADPH serves as a key donor of reductive power for most ROS detoxifying enzymes and can be generated by several metabolic pathways. One source of NADPH reducing power is the NADP-dependent isocitrate dehydrogenase (IDH) reaction. The present study evaluated the properties and regulation of IDH from skeletal muscle of R. sylvatica when frogs were exposed to stress conditions: freezing, dehydration or anoxia. Purified IDH exhibited higher affinity for isocitrate under all stress conditions as compared to controls, suggesting that the enzyme is primed to synthesize NADPH relative to the control state. Immunoblotting showed reduced serine and threonine phosphorylation of muscle IDH from frozen frogs and decreased serine phosphorylation on IDH from dehydrated frogs relative to control and anoxic states, demonstrating a reversible phosphorylation regulatory mechanism for IDH activity during freezing stress. Taken together, these results suggest activation and maintenance of IDH activity despite hypo-metabolic conditions. This initiation in activity of IDH during freezing may play a role in antioxidant defense by contributing to maintenance of the NADPH pool under stress conditions.& COPY; 2023 Elsevier B.V. and Societe Francaise de Biochimie et Biologie Moleculaire (SFBBM). All rights reserved.

Automated summary

The wood frog uses freeze tolerance to survive in cold environments. When exposed to freezing temperatures, the frog's body water can freeze, halting vital functions and causing damage. The study found that an enzyme called NADP-dependent isocitrate dehydrogenase (IDH) plays a role in antioxidant defense by maintaining the NADPH pool under stress conditions. The activity of IDH is regulated through reversible phosphorylation, with reduced phosphorylation observed in frozen and dehydrated frogs compared to controls.