Molecular analysis of inducible Heat shock protein 70 of Pelodiscus sinensis and its effects during pathogen ( Aeromonas hydrophila ) infection

The physiological characteristics and survival of ectotherms are significantly influenced by the environmental temperature. Heat shock proteins (Hsps) are the primary molecular factors that are associated with ectotherm thermal adaption. Heat shock protein 70 (Hsp70) is an important Hsp family member that is involved in many aspects of protein homeostasis and in the immune response. In this study, an inducible Hsp70 homologue (PsHsp70) from the soft-shelled turtle Pelodiscus sinensis was analysed at the molecular level. The recombinant PsHsp70 was purified from Escherichia coli and showed apparent ATPase activity by spectrophotometric assay. The constitutive expression of PsHsp70 was detected in the muscle, liver, kidney, brain, heart and lung by expression assay. The PsHsp70 expression pattern slightly differed in hatchlings incubated at 26°C, 28°C, and 30°C. However, bacterial pathogens induced different levels of PsHsp70 expression in the livers of hatchlings incubated at 26°C, 28°C, and 30°C. Under the harsh temperature of 34°C, the overexpression of PsHsp70 in the pIRES2-EGFP plasmid in turtle embryos did not significantly affect the survival rate of either hatchlings or two-month-old turtles; however, the lysozyme activity significantly differed between hatchlings and two-month-old turtles before bacterial challenge, and the lysozyme activity of both hatchlings and two-month-old turtles changed significantly after bacterial challenge. Taken together, these results suggest that PsHsp70 may play a role in coping with environmental and biological stresses and may be involved in the immune response.