Tissue Damage And Hsp60 Expression In The Tissues Of The Heat Stressed Broilers

The objective of this study was to investigate the association among stress damage and Hsp60 protein and its corresponding mRNA expression in the heart,liver and kidney of the heat-stressed broilers at various stressing times.One hundred broilers were heat stressed for 0h(as control),2h,3h,5h and 10h, respectively,by rapidly increasing the ambient temperature from 22±1℃to 37±1℃. When the heat stress period was over,birds were serially drew blood and slaughtered quickly for sampling.Specimens(heart,liver and kidney) for histopathological and immunohistochemical analysis were fixed in freshly prepared 4%paraformaldehyde in phosphate-buffered saline(pH 7.4),and for quantifying the Hsp60 protein and mRNA levels were frozen in liquid nitrogen and stored at-70℃.The activity of creatine kinase(CK) was significantly increased by heat stress at 2(P＜0.01),3(P＜0.01),5(P＜0.01) and 10 h(P＜0.01) respectively.And the serum glutamic-pyruvic transaminase(GPT) level was remarkably increased at 3(P＜0.05),5(P＜0.01) and 10 h(P＜0.01).After 3 h of heat stress,the parenchyma cells of all tested tissues showed histopathological changes characterized by granular degeneration.Hsp60 expressed mainly in the cytoplasm of parenchyma cells.However,there were no obvious histological lesions in the control group.The intensity of the cytoplasmic staining varied and exhibited an organ-specific distribution pattern.Slight immunolabelling of Hsp60 was observed in the myocardial fibres,the cytoplasm of hepatocytes and the renal tubular epithelial cells.Hsp60 expression was more prominent in the cytoplasm of intact tissue cells than in that of degenerated cells. This maybe linked to tissue damage in response to heat stress.Hsp60 and its corresponding mRNA levels in the hearts showed that the levels of hsp60 mRNA increased sharply(P＜0.01) at 2 h of heat stress but then decreased quickly after 3 h,while the level of Hsp60 protein in the heart increased(P＜0.01) at 2 h of heat stress and maintained a high level throughout heat exposure.Hsp60 fluctuation in the liver and the kidney of heat-stressed broilers gradually decreased at the initiation of heat stress and the lowest Hsp60 levels were both observed at 3 h(P＜0.01).However,hsp60 mRNA expression in liver and kidney stepped up at 1 h(P＜0.01) and 2 h(P＜0.01),respectively.The intensity and distribution pattern of the cytoplasmic Hsp60 staining may be linked to heat stress-induced cellular degeneration.The stress-induced response in terms of hsp60 mRNA and Hsp60 protein levels differed amongst the different tissues and for varying stress treatment times.These results indicate that Hsp60 exert its protective may effect by a tissue-and time-specific mechanism.