Responses of heat shock protein 70 and caspase-3/7 to dietary selenomethionine in juvenile white sturgeon

An 8-week feeding trial was conducted to investigate the responses of juvenile white sturgeon(Acipenser transmontanus) to elevated dietary selenium(Se) based on the determination of the RNA/DNA ratio in muscle, heat shock protein 70(Hsp70), and caspase-3/7 in muscle and/or liver tissues. Four semi-purified test diets were prepared by adding different levels of L-selenomethionine(0, 50, 100, and 200 mg/kg diet). The analytical determinations of total Se were 2.2, 19.7, 40.1, and 77.7 mg/kg diet. The sturgeon(initial body weight: 30 ± 2 g; mean ± SEM) were raised in indoor tanks provided with flow through freshwater(18-19 ℃). There were three replicates for each dietary treatment with 25 fish per replicate.The liver and muscle tissues were collected at 4 and 8 weeks after feeding the test diets. A significant interaction between duration and levels of dietary Se exposures on RNA/DNA ratio in the muscle tissue was detected(P < 0.05). Although there was no significant main effect due to the duration of dietary Se exposures(i.e., 4 weeks versus 8 weeks) on muscle RNA/DNA ratio(P > 0.05), the ratio was significantly decreased with increasing dietary Se levels. Significant main effects were caused by the duration and levels of dietary Se exposures on Hsp 70 in both the muscle and liver tissues, with significant increases in Hsp70 due to a longer exposure(8 weeks) and higher levels(40.1 and 77.7 mg Se/kg diet) of dietary Se.The caspase-3/7 activity in the liver were significantly higher in fish fed the diets containing 40.1 and77.7 mg Se/kg diet than those fed the other diets. The toxic thresholds of Se in the muscle were estimated to be 32.2 and 26.6 mg Se/kg for the depressed specific growth rate and the induced Hsp70 response in muscle, respectively. This result indicated that the Hsp 70 response in muscle is a more sensitive biomarker than the SGR of sturgeon for evaluating Se toxicity in white sturgeon. Results of the current study suggest that a mechanism involved with the activation of stress protein production and apoptosis protects white sturgeon from the lethal effect of Se.