Constitutive and inducible hsp70s are involved in oxidative resistance evoked by heat shock or ethanol

Improved cardiac post-ischemic recovery after whole-body hyperthermia is correlated with an increased expression of the heat shock proteins (hsps). The inducible hsp70 (hsp70i) has a known cardioprotective effect against ischemia/reperfusion injury. Here, we studied whether other hsps are also involved in cardioprotection. Using rat heart-derived H9c2 myocytes, we observed that preheating at 43°C for 20 min conferred resistance to hydrogen peroxide (H₂O₂). The resistance to mild H₂O₂ toxicity (3-5 μmol/10⁷ cells) appeared early and persisted, whereas the resistance to moderate H₂O₂ toxicity (6-9 μmol/10⁷ cells) was detectable only at 20-44 h post heat shock. No resistance was observed at higher doses of hydrogen peroxide (10-12 μmol/10⁷ cells), indicating that severe toxicity exceeds the capacity of the induced protective mechanism. Coincidentally, this thermal regimen elicited a rapid and prolonged increase in the cellular level of hsp70i, and a delayed and transient induction of the constitutive hsp70 (hsp70c). Nuclear translocations of hsp70i and hsp70c also occurred upon heat stimulation. A homogeneous distribution of the accumulated hsp70i and hsp70c throughout the nuclei and cytoplasm paralleled the development of heat-induced resistance to moderate H₂O₂ challenge. Application of another hsp inducer, ethyl alcohol, evoked a similar pattern of H₂O₂ resistance, and hsp induction and distribution. Our results suggest that induction and subcellular distribution of hsp70s contribute importantly to cellular antioxidant defenses, and that a co-operation between hsp70i and hsp70c may improve cardiac preservation during oxidative insult.