Effects of Thermal Stress on the mRNA Expression of SOD, HSP90, and HSP70 in the Spotted Sea Bass (Lateolabrax maculatus)

Abstract

The aim of this study was to elucidate the molecular mechanisms underlying the thermal stress response in the spotted sea bass (Lateolabrax maculatus). Spotted sea basses were exposed to 4 different water temperatures (20, 22, 24, and 28°C) in increasing increments of 2°C/h from 18°C (control) for different time periods (0, 6, 12, 24, 48, 72, and 96 h). Subsequently, 3 tissues (liver, muscle, and gill) were isolated, and the levels of SOD, HSP90, and HSP70 mRNA were assessed. SOD mRNA expression was maintained at baseline levels of control fish at all water temperatures in the liver, while muscle and gill tissue showed an increase followed by a decrease over each certain time with higher water temperature. HSP90 mRNA expression increased in the liver at ≤ 24°C over time, but maintained baseline expression at 28°C. In muscle, HSP90 mRNA expression gradually increased at all water temperatures, but increased and then decreased at ≥ 24°C in gill tissue. HSP70 mRNA expression exhibited an increase and then a decrease in liver tissue at 28°C, but mainly showed similar expression patterns to HSP90 in all tissues. These results suggest the activity of a defense mechanism using SOD, HSP90, and HSP70 in the spotted sea bass upon rapid increases in water temperature, where the expression of these genes indicated differences between tissues in the extent of the defense mechanisms. Also, these results indicate that high water temperature and long-term thermal stress exposure can inhibit physiological defense mechanisms.