Effects of intermittent hypoxia on oxidative stress and protein degradation in molluscan mitochondria

Abstract

Oxygen fluctuations represent a common stressor in estuarine and intertidal environments and can compromise the mitochondrial integrity and function in marine organisms. We assessed the role of mitochondrial protection mechanisms (ATP-dependent and -independent mitochondrial proteases, and antioxidants) in tolerance to intermittent hypoxia or anoxia in three species of marine bivalves: hypoxia-tolerant hard clams (Mercenaria mercenaria) and oysters (Crassostrea virginica), and a hypoxia-sensitive subtidal scallop (Argopecten irradians). In clams and oysters, mitochondrial tolerance to hypoxia (18 h at 5% O 2 ), anoxia (18 h at 0.1% O 2 ) and subsequent reoxygenation was associated with the ability to maintain the steadystate activity of ATP-dependent and -independent mitochondrial proteases and an anticipatory upregulation of the total antioxidant capacity under the low oxygen conditions. No accumulation of endproducts of lipid or protein peroxidation was found during intermittent hypoxia or anoxia in clams and oysters (except for an increase in protein carbonyl concentration after hypoxia-reoxygenation in oysters). In contrast, hypoxia/anoxia and reoxygenation strongly suppressed activity of the ATP-dependent mitochondrial proteases in hypoxiasensitive scallops. This suppression was associated with accumulation of oxidatively damaged mitochondrial proteins (including carbonylated proteins and proteins conjugated with a lipid peroxidation product malondialdehyde) despite high total antioxidant capacity levels in scallop mitochondria. These findings highlight a key role of mitochondrial proteases in protection against hypoxia-reoxygenation stress and adaptations to frequent oxygen fluctuations in intertidal mollusks.

Are the effects induced by increased temperature enhanced in Mytilus galloprovincialis submitted to air exposure?

“…In accordance to our results, Rivera-Ingraham et al (2013) demonstrated that mussels M. edulis presented unaltered protein carbonyl content after reoxygenation, followed by a burst of LPO in same condition. Furthermore, Ivanina and Sokolova (2016) also observed no differences in carbonyl levels in Mercenaria mercenaria clams exposed to anoxia or hypoxia followed by reoxygenation. Thus, the present findings indicate that air exposure during ebb tide did not produce enough stress to generate protein oxidation in mussels.…”

Repeat Exposure to Hypercapnic Seawater Modifies Performance and Oxidative Status in a Tolerant Burrowing Clam

“…In more pronounced hypercapnic and aragonite undersaturated conditions, C. virginica upregulates antioxidant proteins (14 days; ~3500 µatm and 7.5 pH; Tomanek et al, 2011) and a similar response is also seen in the Yesso scallop Patinopecten yessoensis (duration = 14 days; ~2200 µatm, 7.5 pH, and 0.7 Ω; Liao et al, 2019) and mussel Mytilus coruscus (duration = 45 days; ~2800 µatm, 7.3 pH, and 0.5 Ω; Huang et al, 2018). Alternatively, a seemingly 'preparatory' energetic cost of antioxidant synthesis is found in a variety of taxa (Hermes-Lima and Zenteno-Savıń, 2002;Ivanina and Sokolova, 2016) and suggests adaptive energy reallocation to scavenge ROS formed by aerobic recovery when a stressor is lifted.…”

“…Adaptive cellular defense against oxidative damage is thought to have an important evolutionary role in the longevity of the ocean quahog Arctica islandica (lifespan > 400 years) due to a lifestyle of metabolic dormancy (when burrowed) and aerobic recovery (Abele et al, 2008). Further, Ivanina and Sokolova (Ivanina and Sokolova, 2016) found hypoxia-tolerant marine bivalves show anticipatory and compensatory upregulation of antioxidant proteins to mitigate oxidative bursts under hypoxiareoxygenation. Such adaptive responses have yet to be explored under hypercapnic conditions to identify species tolerant to OA stress.…”

Species and tissue specific differences in ROS metabolism to hypoxia- and hyperoxia-recovery exposure in marine sculpins

“…Despite these caveats that come with using MitoB to detect mitochondrial H 2 O 2 , the lack of a direct connection between ROS generation and presumed downstream effects of ROS is not unique to this study and has been observed in other organisms. For example, in molluscs exposed to anoxia+recovery and hypoxia+recovery, changes in aconitase activity (the inhibition of which is directly related to the presence of superoxide) did not mirror changes in total antioxidant capacity nor measures of oxidative damage (Ivanina and Sokolova, 2016). These results illustrate the importance of taking a multifaceted approach to understanding ROS metabolism since measuring only one aspect, e.g.…”

“…In contrast, much less is known about whether animals that inhabit these environments have also evolved strategies to minimize ROS production or mitigate the damaging effects of ROS. Several studies support the idea that hypoxia tolerance is associated with lowered mitochondrial ROS generation (shown in elasmobranchs, mollusks and hypoxia-acclimated killifish Fundulus heterolitus; Du et al, 2016;Hickey et al, 2012;Ivanina and Sokolova, 2016), whereas there does not appear to be a consistent link between hypoxia tolerance and antioxidant defenses in fish (Leveelahti et al, 2014). However, a previous in vitro study of brain mitochondria from multiple species of intertidal sculpin (Cottidae, Actinopterygii) showed that mitochondria from more hypoxia-tolerant species emitted more H 2 O 2 per O 2 molecule consumed under oligomycin-induced state IV conditions compared with a less hypoxia-tolerant species, and H 2 O 2 emitted per mg mitochondrial protein measured did not differ (Lau and Richards, 2019).…”