Role of HSP70 in Cellular Thermotolerance

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 Hsp70-luciferase reporter system in NIH3T3 cells tracked the activation of the Hsp70 gene. Cells in 96-well plates were pretreated in a 43 degrees C water bath for 30 minutes, followed 4 hours later with a severe heat shock at 45 degrees 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 hsp70-containing Murine Embryo Fibroblast (+/+) cells and Hsp70-deficient MEF cells (-/-) through an Arrhenius damage model across varying temperatures (44.5-46 degrees 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 Hsp70-deficient 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 Hsp70-deficient 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. 40:704715, 2008. (c) 2008 Wiley-Liss, Inc.