The warm-adapted Mediterranean blue mussel species Mytilus galloprovincialis invaded southern California during the last century and has since replaced the cold-adapted native M. trossulus from its southern range, possibly due to climate change. Based on previous proteomic analyses, we hypothesized that the more heat-sensitive M. trossulus switches from NADH-producing metabolic pathways that may generate reactive oxygen species (ROS) to NADPH-producing pathways that are able to scavenge ROS during severe heat stress (32°C). We further linked these changes to the activity of the mitochondrial NAD-dependent deacetylase, sirtuin-5, which has been shown to regulate many metabolic pathways. To test the latter hypothesis, we repeated the experiment for both species by exposing gill tissues to 37°C, 28°C, 32°C and 35°C (heating rate of 6°C/h) seawater for 1 h with a subsequent 24 h recovery at 13°C under constant aeration. In a parallel set of incubations we added suramin, a potent sirtuin inhibitor, to characterize the effect of sirtuins on the stress response. Applying a gel-based proteomic analysis and mass spectrometry, we found that sirtuin inhibition affected 19% and 25% of all protein changes during heat stress in the warm-adapted M. galloprovincialis and the cold-adapted M. trossulus (excluding 35°C), respectively. Identified proteins function as molecular chaperones, in proteolysis, signaling, ROS scavenging, energy metabolism, and cytoskeletal dynamics. The number of proteins that were affected by sirtuins doubled in M. trossulus at 35°C, suggesting possible thermal damage of proteins or a role of internal lysine-acetylation in protein degradation as has been shown for N-end lysineacetylation.



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