Abstract
Ectotherms are exposed to a range of environmental temperatures and may face extremes beyond their upper thermal limits. Such temperature extremes can stimulate aerobic metabolism toward its maximum, a decline in aerobic substrate oxidation, and a parallel increase of anaerobic metabolism, combined with ROS generation and oxidative stress. Under these stressful conditions, marine organisms recruit several defensive strategies for their maintenance and survival. However, thermal tolerance of ectothermic organisms may be increased after a brief exposure to sub-lethal temperatures, a process known as "hardening". In our study, we examined the ability of M. galloprovincialis to increase its thermal tolerance under the effect of elevated temperatures (24, 26 and 28 °C) through the "hardening" process. Our results demonstrate that this process can increase the heat tolerance and antioxidant defense of heat hardened mussels through more efficient ETS activity when exposed to temperatures beyond 24 °C, compared to non-hardened individuals. Enhanced cell protection is reflected in better adaptive strategies of heat hardened mussels, and thus decreased mortality. Although hardening seems a promising process for the maintenance of aquacultured populations under increased seasonal temperatures, further investigation of the molecular and cellular mechanisms regulating mussels’ heat resistance is required.
Highlights
Ectotherms are exposed to a range of environmental temperatures and may face extremes beyond their upper thermal limits
Oxidative stress caused by excessive ROS production can lead to cellular damage and eventually cell death, so that mitigation of the oxidative stress via adjustment of mitochondrial ETS activity and/or upregulation of antioxidants plays a key role in the survival and contributes to the costs of cellular homeostasis under heat stress[8,10,11,12,13,14]
The aim of the present study was to investigate whether heat hardening enhances thermal tolerance of M. galloprovincialis, and whether transcriptional and/or post-transcriptional regulation of the pathways involved in mitochondrial energy metabolism, antioxidant defense, and protein quality control are implicated in this phenomenon
Summary
Ectotherms are exposed to a range of environmental temperatures and may face extremes beyond their upper thermal limits Such temperature extremes can stimulate aerobic metabolism toward its maximum, a decline in aerobic substrate oxidation, and a parallel increase of anaerobic metabolism, combined with ROS generation and oxidative stress. Under these stressful conditions, marine organisms recruit several defensive strategies for their maintenance and survival. The mechanisms of heat hardening are not yet fully understood but involve co-activation of multiple stress signaling pathways (including reactive oxygen, nitrogen and carbonyl species, unfolded protein response and transcription factors) that lead to phenotypes with increased resistance[19,20,21,22]. Activation of stress signaling pathways leads to a concerted cellular response at transcriptional and post-transcriptional levels that restore metabolic, proteome, and redox homeostasis, and can protect the organism against subsequent stress impacts[24,25,26,27]
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