The Effect of Selenium on Heat Shock Protein 70 Expression in Turkey Embryos.

Abstract

The optimum incubation environment to obtain the best poult quality has always been an important issue in the turkey industry. Heat shock protein 70 (hsp70) has been associated with the acquisition of thermal tolerance and tolerance to other stressors. Hsp70 functions as a molecular chaperone, assisting in protein refolding after stress-induced denaturation. Selenium is an essential trace mineral and must be incorporated into the enzyme glutathione peroxidase (GPx). GPx functions in the GSH/GSSG-px antioxidant system. It protects cells from damage due to oxidative stress. This study was conducted to examine a potential relationship between dietary supplementation of selenium to turkey hens and the expression of hsp70 in turkey embryos. A total of 52 Nicholas turkey breeder hens were fed either a breeder diet with no supplemental selenium or one supplemented with 0.3ppm organic selenium in yeast (Sel-Plex®, Alltech Inc., Nicholasville, KY). The hens were fed the experimental diets for a minimum of two weeks before the eggs were collected. The eggs were incubated at 37.5°C for 21 days, and the embryos then were heat stressed at 40°C for 2 hr. Liver samples were collected immediately after the termination of the heating episode. The liver samples were analyzed for hsp70 using an immunoblotting procedure. Selenium activity was analyzed by determination of GPx activity. There were no significant differences (P>0.05) between treatment effects on hsp70 expression and GPx activity in embryonic liver samples.

A second experiment was done using commercial breeder flocks. 100 eggs were collected from a non Se-supplemented flock and 90 eggs were collected from a flock, fed 0.3 ppm of organic selenium in yeast (Sel-Plex&#174;, Alltech Inc., Nicholasville, KY). The eggs were incubated for 21 days at 37.5&deg;C and at day 22 half of the eggs were stressed at 40&deg;C and the other half was kept at normal incubation temperatures. The stressed eggs were returned to normal incubator temperatures to recover for 3h. Livers were collected and analyzed as described above. They were compared with the results of the first experiments to see the results. Before stress, hsp70levels were minimal while GPx were at maximal levels with significant GPx levels between treatments. During stress (Experiment 1), there was a non-significant (P>0.05) induction of hsp70 and a significant (P<0.05) decrease of GPx with no significant differences between treatments. After stress hsp70 levels were significantly (P<0.05) higher in the non Se-supplemented samples while the Se-supplemented sample were at pre-stress levels. GPx activity in non Se-supplemented samples did not improve after stress while Se-supplemented samples were significantly (P<0.05) increasing activity after stress.

Hsp70 function is an energy dependent reaction, which protects newly synthesized proteins during and after heat stress. The cell needs to stop normal protein production and divert its energy sources to keep itself alive. Se supplementation helped increase GPx activity before stress. During stress there is a decrease in GPx activity, which induces hsp70. After stress, Se supplementation helped maintain high levels of GPx activity, which reduces oxidative stress, which in turn, the cell does not need long term protection from hsp70, and can resume normal function for embryo development.