Differential proteomic responses of larvae of the marine medaka Oryzias melastigma upon cadmium exposure at thermal extremes

Abstract

Upon facing unpredictable extreme temperature events under the human-driven climate change, marine ectotherms would generally be more susceptible to additional stressors like toxicants. This study aimed to reveal the stress responses in marine medaka larvae Oryzias melastigma upon exposure to cadmium (Cd) under different thermal conditions including extreme temperatures. Larval fish were thermally treated by elevating or decreasing temperatures at a rate of 1ºC per hour followed by 7 days of acclimation to the test temperatures, before commencement of 4 days of Cd treatments. The associated toxic stress responses were elucidated using two-dimensional gel electrophoresis (2-DE) coupled with multivariate statistical analyses. Proteins of fish larvae from temperature treatment groups (i.e., 10ºC, 25ºC and 32ºC) were successfully separated using IEF strip with pH 3-10 and gradient SDS-PAGE with gel percentage of 4-12.5%. The total- and phospho-proteins were visualized using Sypro Ruby and Pro-Q Diamond stains, respectively. Similar numbers of total protein spots (from 206 to 225) were detected in the three temperature treatments. Higher percentage number of phosphoprotein spots was however detected at 10ºC (25%) than at 25ºC (12%) and 32ºC (12%). This observation indicated that alteration of physiological pathways can take place at the low extreme temperature, i.e., 10ºC. In view of the progressive decrease in whole-organism aerobic scope and shift towards anaerobic metabolism under the extreme temperatures, and needs for extra energy for detoxification and cellular repairing processes under chemical exposure, adverse toxic responses could be expected under the extreme temperatures. Proteomic response of the fish larvae under combined Cd and thermal stresses is under investigation. The results of this study could provide certain essential and fundamental information to further advance our understanding on specific toxic effects of trace metals under temperature extremes.