engleski

Seasonal changes in stress-70 proteins content in marine mussel Mytilus galloprovincialis: a field study

Mussels, Mytilus species, are sensitive organisms for biomonitoring of marine environmental contamination due to their wide distribution, abundance, sedentary behaviour, easy of collection and high ability to accumulate heavy metals and organic xenobiotics. Survival and growth of mussel population largely depends on its ability to tolerate the strong fluctuations of environmental factors that can be affected by additional pollution stress. Heat shock proteins also called stress-70 proteins are a family of closely related 70 kDa proteins (HSP70, HSP72, HSC70, HSP75, and GRP78) whose expression is induced following various types of cellular stress. Induction of heat shock proteins (HSPs) appears to increase the resistance, or perhaps facilitate the recovery from stress. This process is very important for aquatic organisms, since it may in turn allow mussels to survive stressors that would otherwise be lethal. In order to elucidate the usefulness of the stress-70 complex induction as biomarker of environmental contamination we investigated contents of stress-70 proteins in gills of natural mussel populations collected from the subtidal rocky shores at different sites of the Rovinj area (Northern Adriatic). Mussels collected during one year (Feb, May, Sep, Dec) from Limski kanal, located about 10 km north of Rovinj were used as unpolluted controls (aquaculture of mussels, oysters and fish), and compared with mussels collected from areas where pollution effects on marine life had been described before. Mussels were taken also from locations near to the local fish cannery, the powerboat fuel station, local harbour and location near the wastewater drain of a tobacco factory. Two stress-70 proteins (HSP70 and HSP72) were detected in the mussel M. gallprovincilis gills after exposure to heat and different model pollutants using 2-D analysis and a monoclonal antibody against bovine HSP70. HSP70 is an inducible and constitutively expressed protein, while and HSP72 is strictly inducible with rare constitutive expression. Induction of stress-70 complex as a response to significant seasonal temperature changes during the year occurred after their acclimatization to low seawater temperature below 11oC during winter months. Maximal contents of HSP72 and HSP70 were observed in natural population of mussels in summer (Sep), and minimal in winter (Dec). Both isoforms of HSPs are constitutively present during the year, with a maximal induction rate of 200%. The highest induction of HSPs was found in mussels near outlets of Fish cannery. Mussels acclimatized to warmer conditions (above 20oC) during summer derived from contaminated sites (Rovinj harbour) reduce HSP72 and HSP70 production in comparison to mussels from reference sites indicating a declined ability of mussels to resists additional pollution stress conditions. We have to point out that significant differences in stress-70 contents in mussels collected at differently contaminated sites compared to unpolluted, control site during four seasons were also detected. The additional effects of pollutants from wastewaters on HSP expressions in mussels might be the explanation for the measured differences. In earlier studies it was shown that the HSPs in Mytilus cells react with differential expression in response to combination of heat and other stressors (model substances). Our findings suggest that the role of inducible HSPs in the physiological and ecological response of mussels to environmental changes has to be further clarify before it is used as a biomarker of environmental exposure or imply in biomonitoring studies. Interesting is the finding that the expression of the both HSP70 and HSP72 kDa proteins are present under natural (nonstressed) conditions and that seasonal changes of environmental parameters or additional heat exposure of mussels can modulate it.

Stress-70 proteins; Heat shock; Environmental pollution; Mytilus galloprovincialis

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