Suppression of reactive oxygen species production enhances neuronal survival in vitro and in vivo in the anoxia‐tolerant turtle Trachemys scripta

Abstract

Hypoxia-ischemia with reperfusion is known to cause reactive oxygen species-related damage in mammalian systems, yet, the anoxia tolerant freshwater turtle is able to survive repeated bouts of anoxia/reoxygenation without apparent damage. Although the physiology of anoxia tolerance has been much studied, the adaptations that permit survival of reoxygenation stress have been largely ignored. In this study, we examine ROS production in the turtle striatum and in primary neuronal cultures, and examine the effects of adenosine (AD) on cell survival and ROS. Hydroxyl radical formation was measured by the conversion of salicylate to 2,3-dihydroxybenzoic acid (2,3-DHBA) using microdialysis; reoxygenation after 1 or 4 h anoxia did not result in increased ROS production compared with basal normoxic levels, nor did H 2 O 2 increase after anoxia/ reoxygenation in neuronally enriched cell cultures. Blockade of AD receptors increased both ROS production and cell death in vitro, while AD agonists decreased cell death and ROS. As turtle neurons proved surprisingly susceptible to externally imposed ROS stress (H 2 O 2 ), we propose that the suppression of ROS formation, coupled to high antioxidant levels, is necessary for reoxygenation survival. As an evolutionarily selected adaptation, the ability to suppress ROS formation could prove an interesting path to investigate new therapeutic targets in mammals.

Short-term anoxic conditioning hormesis boosts antioxidant defenses, lowers oxidative damage following irradiation and enhances male sexual performance in the Caribbean fruit fly, Anastrepha suspensa

“…Similarly, molecular chaperones such as the heat shock proteins (Hsps) also prevent protein aggregation during periods of metabolic suppression, and represent part of the strong cellular defense mounted during hypoxia and anoxia. Hsps are involved in anoxia and oxygen reperfusion events in turtles (Milton et al, 2007) and flies (Liu et al, 2006;Lopez-Martinez et al, 2008;Michaud et al, 2011), as well as in aging (Tower, 2011), where they are thought to prevent oxidative-stress-induced protein denaturing and aggregation. In addition, multiple signal transduction pathways (Insulin, Notch, Toll/lmd, and EGF receptor) that have been associated with stress are upregulated in anoxia tolerance selection lines in Drosophila (Zhou et al, 2008).…”

No oxygen? No problem! Intrinsic brain tolerance to hypoxia in vertebrates

“…Unlike the mammalian brain, which shows an overproduction of reactive oxygen species (ROS) following hypoxia or ischemia/reperfusion (Hashimoto et al, 2003), the turtle brain appears to suppress ROS production upon re-oxygenation (Milton et al, 2007;Pamenter et al, 2007). As with other protective mechanisms, adenosine also impacts the production of ROS upon re-oxygenation (Fig.…”

“…3). Blockade of A1 adenosine receptors increases ROS release and cell death (Milton et al, 2007) despite high levels of antioxidants (Pérez-Pinzón and Willmore and Storey, 1997;Willmore and Storey, 2007). Adenosine effects on ROS may occur in part through Bcl-2, as overexpression decreases cell death during oxidative stress by enhancing antioxidant levels and suppressing free radicals (Lee et al, 2001).…”

Scavenging ROS dramatically increases NMDA receptor whole cell currents in painted turtle cortical neurons

“…1A,Cv), while addition of rotenone during anoxia had no additional effect (−9.1±0.6%; n=4; Fig. 1A ) (Hoyt et al, 1997;Lei et al, 1998;Milton et al, 2007). In addition, this concentration did not affect baseline electrophysiological properties of pyramidal neurons, such as membrane potential, whole-cell conductance and action potential threshold, indicating that it did not induce oxidative damage (Table 1).…”