Heat shock-induced attenuation of hydroxyl radical generation and mitochondrial aconitase activity in cardiac H9c2 cells

Am J Physiol Cell Physiol. 2006 Feb;290(2):C313-24. doi: 10.1152/ajpcell.00362.2005. Epub 2005 Sep 14.


A mild heat shock (hyperthermia) protects cells from apoptotic and necrotic deaths by inducing overexpression of various heat shock proteins (Hsps). These proteins, in combination with the activation of the nitric oxide synthase (NOS) enzyme, play important roles in the protection of the myocardium against a variety of diseases. In the present work we report that the generation of potent reactive oxygen species (ROS), namely *OH in cardiac H9c2 cells, is attenuated by heat shock treatment (2 h at 42 degrees C). Western blot analyses showed that heat shock treatment induced overexpression of Hsp70, Hsp60, and Hsp25. The observed *OH was found to be derived from the superoxide (O(2)(-)*) generated by the mitochondria. Whereas the manganese superoxide dismutase (MnSOD) activity was increased in the heat-shocked cells, the mitochondrial aconitase activity was reduced. The mechanism of O(2)(-)* conversion into *OH in mitochondria is proposed as follows. The O(2)(-)* leaked from the electron transport chain, oxidatively damages the mitochondrial aconitase, releasing a free Fe(2+). The aconitase-released Fe(2+) combines with H(2)O(2) to generate *OH via a Fenton reaction and the oxidized Fe(3+) recombines with the inactivated enzyme after being reduced to Fe(2+) by other cellular reductants, turning it over to be active. However, in heat-shocked cells, because of higher MnSOD activity, the excess H(2)O(2) causes irreversible damage to the mitochondrial aconitase enzyme, thus inhibiting its activity. In conclusion, we propose that attenuation of *OH generation after heat shock treatment might play an important role in reducing the myocardial ischemic injury, observed in heat shock-treated animals.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aconitate Hydratase / metabolism*
  • Animals
  • Cell Line
  • Cell Survival
  • Citrates / metabolism
  • Electron Spin Resonance Spectroscopy
  • Electron Transport / physiology
  • Heat-Shock Proteins / metabolism
  • Hot Temperature*
  • Hydroxyl Radical / metabolism*
  • Mitochondria / enzymology*
  • Myocytes, Cardiac / cytology*
  • Myocytes, Cardiac / metabolism
  • Oxidation-Reduction
  • Rats
  • Spin Labels
  • Superoxide Dismutase / metabolism


  • Citrates
  • Heat-Shock Proteins
  • Spin Labels
  • Hydroxyl Radical
  • Superoxide Dismutase
  • Aconitate Hydratase