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Pharmaceuticals, among them the β-adrenoceptor blocker propranolol, are an important group of environmental contaminants reported in European waters. Laboratory exposure to pharmaceuticals on marine species has been performed without considering the input of the ecosystem flow. To unravel the ecosystem response to long-term exposure to propranolol we have performed long-term exposure to propranolol and low salinity in microcosms. We applied shotgun proteomic analysis to gills of Mytilus edulis from those Baltic Sea microcosms and identified 2071 proteins with a proteogenomic strategy. The proteome profiling patterns from the 587 highly reproductive proteins among groups define salinity as a key factor in the mussel's response to propranolol. Exposure at low salinity drives molecular mechanisms of adaptation based on a decrease in the abundance of several cytoskeletal proteins, signalling and intracellular membrane trafficking pathway combined with a response towards the maintenance of transcription and translation. The exposure to propranolol combined with low salinity modulates the expression of structural proteins including cilia functions and decreases the expression of membrane protein transporters. This study reinforces the environment concerns of the impact of low salinity in combination with anthropogenic pollutants and anticipates critical physiological conditions for the survival of the blue mussel in the northern areas. Biological significance Applying shotgun proteomic analysis to M. edulis gills samples from a long-term microcosm exposure to propranolol and following a proteogenomic identification strategy, we have identified 2071 proteins. The proteomic analysis unrevealed which molecular mechanisms drive the adaptation to low salinity stress and how salinity modulates the effects of exposure to propranolol. These results reinforce the idea of the impact of low salinity in combination with anthropogenic pollutants and anticipate critical physiological condition. [ABSTRACT FROM AUTHOR]

Osmoregulation is a vital physiological function for fish, as it helps maintain a stable intracellular concentration of ions in environments of variable salinities. We focused on a primarily freshwater species, the European whitefish ( Coregonus lavaretus), to investigate the molecular mechanisms underlying salinity tolerance and examine whether these mechanisms differ between genetically similar populations that spawn in freshwater vs. brackishwater environments. A common garden experiment involving 27 families in two populations and five salinity treatments together with a large-scale, high-resolution mass spectrometry experiment that quantified 1500 proteins was conducted to assess phenotypic and proteomic responses during early development, from fertilization until hatching, in the studied populations. The populations displayed drastically different phenotypic and proteomic responses to salinity. Freshwater-spawning whitefish showed a significantly higher mortality rate in higher salinity treatments. Calcium, an ion involved in osmotic stress sensing, had a central role in the observed proteomic responses. Brackishwater-spawning fish were capable of viable osmoregulation, which was modulated by cortisol, an important seawater-adaptation hormone in teleost fish. Several proteins were identified to play key roles in osmoregulation, most importantly a highly conserved cytokine, tumour necrosis factor, whereas calcium receptor activities were associated with salinity adaptation. These results imply that individuals from these populations are most likely adapted to their local environments, even though the baseline level of genetic divergence between them is low ( FST = 0.049). They also provide clues for choosing candidate loci for studying the molecular basis of salinity adaptation in other species. Further, our approach provides an example of how proteomic methods can be successfully used to obtain novel insights into the molecular mechanisms behind adaptation in non-model organism. [ABSTRACT FROM AUTHOR]