Multiple stressor responses are regulated by sirtuins in Mytilus congeners

Understanding physiological tolerances of marine organisms to environmental stress is key to predicting species susceptability under climate change. Along the Pacific Coast of the U.S.A. intertidal mussel congeners (genus Mytilis) vary in their physiological stress tolerances, with the invasive M. galloprovincialis being heat tolerant but vulnerable to hyposalinity while the native M. trossulus is vulnerable to heat stress and tolerant of hyposalinity. Sirtuins, a family of NAD(+)-dependent deacylases, may influence the environmental stressor tolerances in these mussel congeners. The purpose of our study was to determine the mechanism by which sirtuins may confer differential stress responses in the two mussel congeners. Mussels (N = 6 per species) were acclimated to laboratory conditions in tidal simulators and exposed to sirtuin inhibitors (suramin and nicotinamide). Following inhibition, mussels were exposed to hyposalinity stress (29 ppt) for 6 h followed by aerial heat stress (32 degrees C) for 6 h after which mussel gill was dissected for proteomic analysis. During sirtuin inhibition we found a reduction of cellular stress response (CSR) proteins (molecular chaperones, antioxidants), which are key to maintaining cellular homeostasis. Moreover, we found differential stress responses between the two species under aerial heat combined with hyposalinity exposure. Three-way interactions (aerial heat, hyposalinity and sirtuin inhibition combined) showed complex interactive effects with sirtuins as potential modulators. Thus, our study suggests that sirtuins are contributing to the species-specific CSR in Mytilus and our multiple-stressor approach provides information used to make predictions regarding climate change effects on these competing species.