Abstract
Background and Objective
Thermal pretreatment has been shown to condition tissue to a more severe secondary heat stress. In this research we examined the particular contribution of heat shock protein 70 (HSP70) in thermal preconditioning.
Study Design/Materials and Methods
For optimization of preshock exposures, a bioluminescent Hsp70βluciferase reporter system in NIH3T3 cells tracked the activation of the Hsp70 gene. Cells in 96βwell plates were pretreated in a 43Β°C water bath for 30 minutes, followed 4 hours later with a severe heat shock at 45Β°C for 50 minutes. Bioluminescence was measured at 2, 4, 6, 8, and 10 hours after preshock only (PS) and at 4 hours after preshock with heatshock (PS+HS). Viability was assessed 48 hours later with a fluorescent viability dye. Preshock induced thermotolerance was then evaluated in hsp70βcontaining Murine Embryo Fibroblast (+/+) cells and Hsp70βdeficient MEF cells (β/β) through an Arrhenius damage model across varying temperatures (44.5β46Β°C).
Results
A time gap of 4 hours between preconditioning and the thermal insult was shown to be the most effective for thermotolerance with statistical confidence of P<0.05. The benefit of preshocking was largely abrogated in Hsp70βdeficient cells. The Arrhenius data showed that preshocking leads to increases in the activation energies, E~a~, and increases in frequency factors, A. The frequency factor increase was significantly greater in Hsp70βdeficient cells.
Conclusion
The data shows that HSP70 contributes significantly to cellular thermotolerance but there are other pathways that provide residual thermotolerance in cells deficient in Hsp70. Lasers Surg. Med. 40:704β715, 2008. Β© 2008 WileyβLiss, Inc.