Modulation of Thermal Stress Response by Prostaglandins in Gills of the Blue Mussel Mytilus Edulis

Mytilus edulis has experienced massive mortality events associated with thermal stress that have been documented in wild as well as cultivated organisms, since this species is traditionally farmed in intertidal areas that are exposed to temperature variations. The stress responses linked to changes in temperature are modulated by prostaglandins (PG), which induce apoptosis, synthesis of heat shock proteins and antioxidant enzymes, among others. PG are mainly synthesized from arachidonic (ARA), eicosapentaenoic (EPA) and docosahexaenoic (DHA), but PG-like compounds can be produced through non-enzymatic oxidation of fatty acids in response to increased reactive oxygen species (ROS). In this study, we applied acute (a single temperature increase of 13 degrees C, from 12 degrees C to 25 degrees C) or chronic (cyclical temperature increases and decreases of 13 degrees C for eight days) thermal stress to mussels fed a microalga mix of Nannochloropsis oculata and Pavlova lutheri. The response was quantified by measuring PG produced enzymatically by cyclooxygenase (COX) from ARA, EPA, and DHA (PGE2, PGE3, 13HDHA, respectively), non-enzymatic PG (13,14-dihydro-15-keto-PGE2 PGF3 alpha and 8-isoprostane). PGE2, PGE3, and 13-HDHA levels were higher in the gills of mussels exposed to acute stress compared to chronic stress while 3,14-dihydro-15-keto-PGE2 showed no significant differences as a result of chronic or acute stress. PGF3 alpha had lower levels in mussels exposed to chronic stress compared to those under acute stress. In contrast, 8-isoprostane was significantly higher in mussels exposed to chronic stress compared to acute stress. Mussels exposed to acute stress showed an increase in hemocyte infiltration in the gills, while those exposed to chronic stress showed a decrease in gill filament width compared to mussels submitted to acute stress; both effects are associated with PG modulation. These findings suggest that acute and chronic stressors have distinct effects on lipid composition, prostaglandin levels, and gill filament morphology, highlighting potential adaptations or responses to different stress conditions. Understanding the mechanisms by which PG and PG-like compounds modulate the thermal stress response in mussels will contribute to the understanding of climate change impacts on bivalves and the possible adaptation processes involved.