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% O2), anoxia (18 h at 0.1% O2) and subsequent reoxygenation was associated with the ability to maintain the steady-state 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 end-products 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 hypoxia-sensitive 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.
The authors declare no competing or financial interests.
Conceptualization, A.V.I. and I.M.S.; Methodology, A.V.I. and I.M.S.; Investigation A.V.I.; Writing – Original Draft, I.M.S. and A.V.I.; Writing – Review & Editing, I.M.S. and A.V.I., Funding Acquisition, I.M.S.; Formal Analysis, A.V.I. and I.M.S.
This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
- Received July 13, 2016.
- Accepted September 16, 2016.
- © 2016. Published by The Company of Biologists Ltd